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This is to certify that the
thesis entitled

HEXANE-BASED NINHYDRIN RINSE FOR LATENT PRINT
ENHANCEMENT ON PLASTIC MATERIALS FOLLOWING
APPLICATION OF BLACK POWDER

presented by
KELLIE LEA KINCAID

has been accepted towards fulﬁllment
of the requirements for the

MS. degree in Forensic Science

 

 

 

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HEXANE-BASED NINHYDRIN RINSE FOR LATENT PRINT ENHANCEMENT ON
PLASTIC MATERIALS FOLLOWING APPLICATION OF BLACK POWDER

By

Kellie Lea Kincaid

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of
MASTER OF SCIENCE

School of Criminal Justice

2005

ABSTRACT

HEXANE-BASED N INHYDRIN RINSE FOR LATENT PRINT ENHANCEMENT ON
PLASTIC MATERIALS FOLLOWING APPLICATION OF BLACK POWDER

By

Kellie Lea Kincaid

Plastic items can be difﬁcult to process for latent prints using black powder as the
prints become engulfed in powder and any ﬁngerprint ridge detail can be lost. In the
research presented, over 100 plastic items and nearly 300 ﬁngerprints were tested to
examine what plastic characteristics result in an enhanced print when the powdered print
was washed with a ninhydrin hexane solution. Features such as plastic type, inked
printing, presence or absence of labels, color, surface ﬁnish, surface tension, and surface
roughness were analyzed to evaluate their inﬂuence on the rinsing method success.
Microscopic examinations were made using Scanning Electron Microscopy to identify
the changes that occurred to the print between the cycles of powdering‘ and rinsing.
Scanning Electron Microscopy — Energy Dispersive X-Ray Spectrometry was used to
examine the chemical interactions among the plastic, cyanoacrylate, black powder, and
rinsing solution. High-density polyethylene plastic containers and bags demonstrated a
strong success in enhancing latent prints after becoming engulfed in black powder.
Rough textured surfaces tended to beneﬁt from the rinsing solution. Inked surfaces
typically had a lower success rate than those surfaces with a label or where a label had
been removed. Results show that the powder/rinsing technique can act as another layer of

latent print processing when other methods of enhancement have failed or powdering has '

obscured a print.

Copyright by
KELLIE LEA KINCAID

2005

Acknowledgements

I would like to thank David Foran, Ph.D. from Michigan State University
Forensic Science Program for his time and support in helping design this research
experiment. He provided encouragement and guidance for conducting a thorough study
ensuring that all aspects of the research were addressed. I appreciate all of the long hours
he has put in for editing and revising this thesis as well.

I would also like to thank Kathy Boyer of the Michigan State Police Latent Print
Unit in Bridgeport for her conﬁdence and trust in providing me with her newly developed
latent print processing technique to further research and study. She provided much
support and guidance that was needed for this latent print study.

I would also like to thank the individuals at the Michigan State Police Latent Print
Unit in Lansing for their support and teaching of ﬁngerprinting techniques. I appreciate
them allowing me to conduct my research and to utilize their supplies for this project.
The individuals include: Greg Michaud, Michele Glasgow, Gary Daniels, Derek Emme,
Scott Hrcka, Bob May and Jim Voss.

I would like to thank Susan Selke, PhD. of the Michigan State University
Packaging Program for her information regarding plastic materials, and Reza Loloee,
Ph.D. from the Michigan State University Physics Department for teaching and allowing
me to operate the Dektak IIA proﬁlometer.

In addition, thank you to those individuals from the Center for Advanced

Microscopy of Michigan State University including Shirley Owens, Ewa Danielewicz

iv

and Carol Flegler for providing additional help and support when using the Scanning
Electron Microscope.

I would like to thank all of my friends who have helped to make this Masters
program a fun and exciting experience. They provided unconditional support and
encouragement to keep working hard in order to achieve my degree. Also, thank you goes
to those friends who donated the plastic materials of which were used in this research.

Thank you to Brian Johnson for his assistance in computer related issues
including. I appreciate his positive attitude and encouragement.

I would like to thank Scott Krejci for his support and constant reassurance that no
obstacle was too great, and that I can accomplish anything that I set my mind to.

Most importantly, I would like to thank my parents and family for their never
ending support both spiritually and ﬁnancially to make this educational journey a great
learning experience. They managed to lift my spirits when times seemed overwhelming
and were able to always ensure that I kept striving toward the goals that I set out to
achieve. I truly appreciate each time they have been there for me and all that they have
done.

Thank you also goes to Max, Zoom and Berlin, my dogs, for helping to relieve the

stress of graduate school. They helped to keep me happy.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................... ix

LIST OF FIGURES ................................... x

Introduction ......................................................................................................................... l
Anatomical Development of Fingerprints ................................................ 1
Individualization of Fingerprints for Identiﬁcation ..................................... l
Fingerprinting Pioneers ...................................................................... 3
Fingerprint Individuality ...................................................................... 4
Latent Fingerprints ........................................................................... 5

Latent Fingerprint Processing Techniques

Latent Prints on Non-Porous Materials .......................................... 6
Latent Prints on Porous Materials ................................................ 8
Fingerprint Processing Sequence..................................... .................... 10
Difﬁcult Substrates for Powdering ...................................................... ll

Characterization of Fingerprint Adhesion on Plastics
Surface Tension Analysis ........................................................ l4
Microscopy Characteristics of Fingerprints .................................... l4

Scanning Electron Microscopy — Energy Dispersive X-Ray

Spectrometry ................................................................................... 15

Proﬁlometry ........................................................................ 16
Background on the Research Presented Here ........................................... 16
Research Goals .............................................................................. 16

vi

Materials and Methods ....................................................................................................... 17

Sample Collection ........................................................................... l7
Rinsing Solution ........................................................................... 18
Sample Processing ......................................... t ................................ 18
Rinse Solution Analysis ................................................................... 20

Instrumental Techniques
Surface Tension Determination ................................................. 2]
Scanning Electron Microscopy .................................................. 21

Scanning Electron Microscopy — Energy Dispersive X-Ray

Spectrometry ................................................................................... 22

Proﬁlometry ........................................................................ 22
Results ................................................................................................................................ 23
Rinsing Technique Evaluation ............................................................ 23
Processing Identiﬁable Prints ............................................................ 34
Effect of Plastic Variables on Fingerprint Enhancement ............................. 36
Plastic Types ....................................................................... 36

Plastic Color ........................................................................ 37
Surface Finish ...................................................................... 38

Inked Printing and Adhesive Analysis .......................................... 38
Surface Tension ................................................................... 39
Proﬁlometry ........................................................................ 41
Cyanoacrylate Chamber Results ......................................................... 42
Inter-Individual Variability Analysis .................................................... 42
Rinse Solution Variation Analysis ....................................................... 43

vii

Microscopic Analysis of Enhancement Progression
Scanning Electron Microscopy .................................................. 44
Elemental Analysis of Enhancement Progression

Scanning Electron Microscopy - Energy Dispersive X—Ray

Spectrometry .................................................................................... 47
Discussion ............................................................................................ 49
Item Collection and Sample Sizes ....................................................... 50
Processing Results ......................................................................... 50
Plastic Types ................................................................................ 51
The Inﬂuence of Color ..................................................................... 51
The Inﬂuence of Surface Finish and Surface Roughness ............................. 52
The Inﬂuence of Inked Printing and Adhesives ....................................... 54
The Inﬂuence of Surface Tensions ...................................................... 55
Processing Variations ...................................................................... 56
Rinsing Solution Component Analysis .................................................. 56
Scanning Electron Microscopy Analysis ................................................ 57
Scanning Electron Microscopy — Energy Dispersive X-Ray Spectrometry
Analysis ............................................................................. 58
Potential Mechanisms of the Rinsing Method ................................................... 60
Overall Recommendations and Observations ................................................... 62
APPENDICES
APPENDIX A: Sample Characterizations and Processing Results .................. 65
APPENDIX B: Surface Tension and Plastic Type Processing Results .............. 78
REFERENCES ....................................................................................... 81

viii

LIST OF TABLES

Table 1: Plastic Identification Table .............................................................. 12
Table 2: Rinsing Solution Chemicals............................; ............................... 20
Table 3: Sampling Stages ........................................................................... 22
Table 4: Processing Results .......................................................................... 24
Table 5: Initially Identiﬁable Latent Prints ...................................................... 35
Table 6: Plastic Type Enhancement Success Rates ............................................. 36
Table 7: Color Analysis ............................................................................. 37
Table 8: Surface Finish Analysis .................................................................. 38
Table 9: Inked Printing/Adhesive Analysis ...................................................... 39
Table 10: Surface Tension Readings ............................................................ 40
Table 11: Proﬁlometer Analysis .................................................................. 41
Table 12: Rinsing Solutions Results ......................................... . .................... 44

Figure 1:
Figure 2:
Figure 3:
Figure 4:
Figure 5:
Figure 6:
Figure 7:
Figure 8:
Figure 9:
Figure 10:
Figure 11:
Figure 12:
Figure 13:
Figure 14:
Figure 15:
Figure 16:
Figure 17:
Figure 18:
Figure 19:
Figure 20:

Figure 21:

LIST OF FIGURES

Anionic Polymerization of Cyanoacrylate ............................................ 7
Ruhemann’s Purple Reaction ......................... ‘ ................................. 9
Enhanced Print on Sample #96—a .................................................... 25
Enhanced Print on Sample #79 ........................................................ 25
Enhanced Print on Sample #78-a ...................................................... 26
Enhanced Print on Sample #45-b ..................................................... 26
Enhanced Print on Sample #32-a .................................................... 26
Enhanced Print on Sample # 32—b .................................................... 27
Enhanced Print on Sample #32-c ................. ' .................................... 27
Enhanced Print/Lost Detail on Sample #1 l-c ..................................... 28
Enhanced Print/Lost Detail on Sample #101-a .................................... 28
Enhanced Print/Lost Detail on Sample #87-a ..................................... 29
Enhanced Print/Lost Detail on Sample #95-c ..................................... 29
Lost Print/Detail on Sample #28-c .................................................. 30
Lost Print/Detail on Sample #69-b .................................................. 30
Black Powdered on Sample #74-a ................................................... 31
Black Powdered on Sample #33-a ............ 31
Black Powdered on Sample #56-a ................................................... 32
Lost Print/Blurred on Sample #62—a ................................................. 32
Print Remaining/No Black Powder Surrounding on Sample #102-b ........... 33
Lost Print/Black Powder Surrounding on Sample #13-e ........................ 34

Figure 22:
Figure 23:
Figure 24:
Figure 25:

Figure 26:

Lost Print/Black Powder Surrounding on Sample #15-c ......................... 34
SEM Images of Multiple Prints ...................................................... 45
SEM Images of a Single Print ....................................................... 46
SEM-EDS Cyanoacrylate Fumed Print — Ridge and Furrow .................... 48
SEM-EDS Cyanoacrylate Fumed Print — Ridge 1 and Ridge 2 ................. 49

xi

Introduction

Forensic science is the application of science to criminal justice in an effort to
assist in answering civil and criminal questions. The study of ﬁngerprints, or
dactylography, has been useful in answering these questions. Fingerprint processing is
probably one of the most well known forensic techniques and typically among the ﬁrst
evidentiary items that crime scene investigators will search for at a scene (Beckman
2001). Latent print processing gives investigators direction for solving these questions
and it also helps to identify and associate individuals with evidence or crime scenes.
Anatomical Development of Fingerprints

To better understand the basic importance of ﬁngerprint classiﬁcation and
identiﬁcation, it is necessary to understand how ﬁngerprints develop and what makes
them unique. Friction ridge skin, formed in unique patterns of ridges and furrows, is
found on the soles of the feet, palmar surfaces, and ﬁngers. The ridges comprise the
raised areas of the skin where the sweat pores are located while the furrows make up the
space between the ridges helping to distinguish the rows of ridges (Coppock 2001). The
spatial relationships of the ridges and furrows are fully developed at birth and remain
unchanged throughout life, changing only in size during aging, unless damage has been
done to the dermal layer through scars or burns. This permanence and uniqueness help to
make ﬁngerprints a very valuable piece of evidence.

Individualization of Fingerprints for Identiﬁcation

There are three levels of detail that help in ﬁngerprint identiﬁcation. The ﬁrst

consists of the pattern type or the pattern of ridge ﬂow, the second involves the individual

ridge characteristics such as enclosures, ridge endings and bifurcations, and the third

involves identiﬁcation by pore conﬁguration and ridge shapes (Parsons et al.). General
ﬁngerprint patterns can be divided into three different groups. The simplest of these is the
arch, comprising about 5% of all ﬁngerprints, is further divided into the plain arch and
tented arch. The plain arch is a ridge ﬂow from side to side With a peak in the center,
while the tented arch consists of the same side to side ﬂow except the ridges have an up
thrust at a 45 degree angle or greater near the center of the pattern. A second ﬁngerprint
pattern is the loop, comprising about 65% of all pattern types. The loop pattern is deﬁned
by two structures, the core and the delta, where the core is the center of the pattern and
the delta is the characteristic nearest the point of two diverging ridges. This type can be
described as radial or ulnar when in reference to a particular hand or a ten-print
ﬁngerprint card. The radial loop is a pattern where one or more ridges ﬂow from one
side, recurve and either touch or pass an imaginary line between the core and retreat to
the side where the ridges entered, in this case the side of the hand where the radial bone is
located. The same rule applies to the ulnar loop. If there is no reference to the hand of
where the ﬁnger was, it is simply called a left or right slanted loop (SWGFAST
http://www.swgfast.org/Glossarv Consolidated ver l.pdf ).
The last ﬁngerprint pattern, the whorl, deﬁned as having at least two deltas with
recurving ridges between them, comprise about 25 — 35% of all ﬁngerprint patterns.
Whorls can be divided into four sub-pattems: the plain whorl, central pocket whorl,
double loop, and accidental whorl (Coppock 2001).

The second level of detail in ﬁngerprint identiﬁcation involves the analysis of
friction ridge characteristics, also called minutiae. These include the ending ridge,

bifurcation, dot, enclosure, short ridge, right angle intersection, bridge, spur, and

triradius. In a forensic context, these minutiae are examined in a spatial relationship by
noting the location and number of intervening ridges between minutiae points. Minutiae
are generally the characteristics that make ﬁngerprints unique however, the exact number
of minutiae required to individualize a ﬁngerprint is a source of ongoing debate (Stacey
2005).

The third level of fingerprint detail involves poroscopy, the study of pore
structures along friction ridge skin, and edgeology, the study of edge structures on
friction ridge skin. Pores line the ridges and secrete sweat, which helps to leave the
impression of the ﬁngerprint behind. Combining both poroscopy and edgeology help to
identify or eliminate the fingerprint in question however, in many instances this level of
detail is not always present or clear on latent prints (Coppock, 2001).

Fingerprinting Pioneers

There were several people who assisted in discovering the importance of
ﬁngerprints and their role in identifying individuals. Lee and Gaensslen (1991) have
detailed the history of ﬁngerprint identiﬁcation methods and those individuals who were
responsible for recognizing them. Johannes Purkinje is thought to be responsible for the
ﬁrst modern study of ﬁngerprints when in 1823 he proposed a system of ﬁngerprint
classiﬁcation however, it had little response from law enforcement agencies or the
community. During the second half of the 19'h century, Sir William Herschel became the
ﬁrst to conﬁrm that the ridges that develop on the hands and feet while in the womb do
not change unless there is injury done deep in the muscles and tissues. At about the same
time, a Scottish doctor in Japan, Henry Faulds, was asked to help in an investigation

where ﬁngerprints had been left in soot at the scene. This became the ﬁrst case in which

ﬁngerprint evidence was used to solve a crime. As a result of this discovery, Faulds wrote
to Charles Darwin requesting aid in obtaining ﬁnger impressions of lemurs, anthropoids,
etc. Darwin responded to Faulds by directing him to Sir Francis Galton, which ultimately
led to Galton’s study on the uniqueness of ﬁngerprints, and in the late 19th century,
Galton began using ﬁngerprints as a means of identiﬁcation. He wrote a detailed study of
ﬁngerprints in which he presented a new classiﬁcation system using prints of all ten
ﬁngers, which is the basis for identiﬁcation systems still in use. Sir Edward Richard
Henry used his knowledge of ﬁngerprinting in the 1890s to assist the police in Bengal,
India to identify criminals. As assistant commissioner of the metropolitan police, Henry
applied methods developed by Galton to establish the ﬁrst British ﬁngerprint ﬁles in
London in 1901 (Lee and Gaensslen 1991). This ﬁling system became the greatest means
for identiﬁcation, surpassing the Bertillion system which previously had been a method
of personal identiﬁcation using various body location measurements.
Fingerprint Individuality

Although ﬁbers, paint, shoe and tire impressions can be left behind to associate
the criminal with the crime scene, a ﬁngerprint uniquely places the suspect at a scene.
Even DNA evidence, which is generally individualizing, can be shared by individuals if
they are identical twins. In contrast, because ﬁngerprints have both a genetic component
and environmental component, identical twins, while having similar ﬁngerprints, can still
be differentiated through points of minutiae. Likewise other family members are likely to
have prints more similar to each other than to unrelated individuals, but also can be

distinguished (Richards).

Latent Fingerprints

Fingerprints can be a means for identiﬁcation and individualization however,
knowing this is of no value unless a ﬁngerprint from a crime scene is available for
comparison with a known print. Through the commission of a crime, criminals may leave
behind a latent print: a print that is present but is not visible and must be developed or
enhanced for collection and comparison purposes. Latent prints are primarily composed
of sweat, oils, and amino acids that are exuded from the pores and deposited on any
surface to which the ﬁnger comes in contact. Other materials such as cooking oil, hair oil,
and hand cream can also be left behind giving the shape and characteristics of the latent
prints. It is also important to note that not all latent prints are a result of material that is
left behind; they can result from removing material such as powder or dust from the
surface as well (Cowger 1993).

Latent prints can be deposited onto a number of different surface types, either
porous, semi-porous or non-porous, and thus require different processing procedures.
Although there is a range of materials that are conducive to latent ﬁngerprint
enhancement, porous surfaces, those that allow gases and liquids to pass through, are
better able to preserve the latent ﬁngerprint for comparison. Examples of porous
materials include paper, cardboard, or unﬁnished wood. Semi-porous materials such as
wood, concrete, glossy labels, photographs, and glossy magazines, allow liquids or gases
to penetrate but not pass through. Finally, non-porous materials do not allow liquids or
gases to pass through. Latent prints left on these media are typically less conducive to

preservation because the print resides on the surface and is exposed to further contact or

destruction. Examples of non-porous materials include glass, ﬁnished wood, firearms,
plastic bags, and plastic bottles.

Latent Fingerprint Processing Techniques

Latent Prints on Non-Porous Materials

Although latent prints may be present on the item of interest, without
enhancement techniques, they are of no value. Whether processing a crime scene or
evidence, powdering is one of the simplest forms of latent print development. Powdering
ﬁngerprints, for both semi-porous and non-porous materials, is employed for its
effectiveness in enhancing latent prints and capturing minutiae for identiﬁcation. This
technique has been used for latent ﬁngerprint development since the early nineteenth
century. The powder helps enhance the latent print by adhering to its moisture and
organic contaminants, helping in visualization of ridge detail (Lee and Gaensslen 1991).
There are various colors of powders, including the more traditional black, white, and
silver. These are chosen based on the contrast in color between the powder and the
evidentiary item. Unfortunately, while many items are enhanced by the powdering
process, others react negatively by blurring or engulﬁng the latent print to the point of
obscuring them.

When latent prints are to be developed on multicolored, nonporous surfaces, a
ﬂuorescent powder may prove useful. These powders help when ordinary colored
powders do not produce contrast along the entire latent print. To visualize the print, an
ultraviolet light is used to make the powder ﬂuoresce, eliminating the background
distraction. A third type of powder includes the magnetic kind, which are comprised of

very thin shavings of colored magnet. The magnetic powder is chosen due to its

nondestructive nature where the brush never comes in contact with the latent print. This
powder is ideal for developing latent prints on porous surfaces such as raw wood, paper,
and leather, and is also useful for applying to the undersides and sides of objects where
normal powders are not effective (Moennsen 1971).

Powdering may be preceded by cyanoacrylate fuming, a technique for processing
semi-porous and non-porous materials to stabilize the latent ﬁngerprint and assist in
visibility. Cyanoacrylate, C5H5N02, commercially known as Superglue, was ﬁrst
employed in 1978 by the Criminal Identiﬁcation Division of the Japanese National Police
Agency (Brown 1990). When the cyanoacrylate is vaporized, it reacts with moisture and
adheres to amino acids and organic components of the latent ﬁngerprint, polymerizing on
the ﬁngerprint ridges, resulting in a hard white outline (Margot and Lennard 1994). In the
presence of a weak base, cyanoacrylate undergoes anionic polymerization, and then
becomes stabilized with the addition of a weak acid. When the cyanoacrylate comes into
contact with a surface, weak bases, such as water or alcohol, can act to neutralize any
acid stabilizer that may be present and speed up the polymerization (Courtney and
Verosky 1999). Figure 1 displays the anionic polymerization that cyanoacrylate
undergoes in the presence of water.

F_igure 1 Anionic Polymerization of Cyanoacrylate

 

H—O\ =< —+ p—CHrle —+ Polycyanocarylate
H (3:0 H Ic=o
0’ o
\ \
CH3 CH3

 

 

 

With the addition of water, cyanoacrylate undergoes anionic polymerization.
(http://wwwdevicelink.com/mddi/archive/99/09/006.html)

Several dye stains can be used following cyanoacrylate fuming to further enhance
latent prints. One of these is ardrox, a ﬂuorescent dye that has proven effective for latent
print processing on non-porous items, making weakly developed latent prints more
visible against a background with an array of colors. When illuminated with an ultraviolet
lamp or ﬂuorescent light source, these prints ﬂuoresce brightly and are easily seen for
photography and identiﬁcation. A number of other ﬂuorescent dyes, such as Rhodamine
6G, R.A.M. (rhodamine, ardrox and methanol), and R.A.Y. (rhodamine, ardrox and basic
yellow 40), can be used in combination with cyanoacrylate fumed prints to assist in
visualization (Chesepeake Bay Division of the International Association for
Identiﬁcation, http://www.cbdiai.org/). The latent prints processed with these dyes are
visualized with ﬂuorescent light sources of various wavelengths such as lasers, Polilights,
and Ruvus. These commercially available light sources are effective due to their ability to
alternate the wavelengths of light that are directed across the sample, displaying different
degrees of clarity for the latent ﬁngerprint.

Latent Prints on Porous Materials

Ninhydrin (1,2,3-tri-keto-hydrindene hydrate), in the 1950’s was discovered to be
a valuable tool for processing porous items for latent prints, where it reacts with amino
acids (W ertheim). The reaction between ninhydrin and amino acids (Figure 2) produces a
colored product, known as Ruhemann’s purple. The speed of the reaction can be

increased in a humidity chamber (Lee and Gaennslen 1991).

Figure 2 Ruhemann’s Purple Reaction

9 (.3 R c {
l ; ‘-
O OH ______ O H._.N—CHCOO ﬂ
......_.. o__—_.__+ ’N-C
OH .
R
o c") 3
Ninhydrin
o} 0
—CO N=CHR
—-———i’——,. N£HR :2: H
HIBH O
o
. I
innit: ['1
M
-—RCHO

Ruhemann’s purple

The chemical reaction that occurs between ninhydrin and an amino acid to yield the end
product, Ruhemann’s Purple (Lee and Gaennslen 1991).

Over the years, the solution in which the ninhydrin is dissolved has included
components such as acetone or heptane, whereas more recently, laboratories have begun
altering the solution to help eliminate inks on porous evidence from running, which often
occurred with the earlier solutions. Scarborough (2001) developed a ninhydrin solution
containing ninhydrin, methanol, ethyl acetate and hexane that has helped to alleviate this

problem.

The Chesapeake Bay Division of the International Association for Identiﬁcation’s
website lists a number of techniques for processing porous items. The ﬁrst is silver
chloride, which is the oldest chemical technique for uncovering latent prints. Silver
chloride reacts with the chloride component of the print however, its use has diminished
as it is only effective on fresh ﬁngerprints. Further, silver chloride reacts with the
substrate, producing a dark background that can obscure the print. Other
techniques/chemicals such as iodine fuming and 5-Methylthioninhydrin (5-MTN) are
used for processing porous items as well. Fluorescence techniques include 1,8
Diazaﬂuoren-9-one (D.F.O.), which reacts with the amino acid component of the latent
print, developing more ridge detail than ninhydrin. 1,2-Indanedione, in combination with
forensic light sources, yields ﬂuorescing ridges. Porous items that have been wet can be
processed with physical developer by applying the solution over ninhydrin if the latter
was not successful in enhancing the print.

Fingerprint Processing Sequences

Depending on the porosity of the material, different sequential steps will be taken
for processing non-porous items (which are the focus of the research below). First, an
examination of the item is completed for any visible prints, and photographs are taken to
ensure documentation of prints in the chance that any alteration or erasure of the
ﬁngerprint occurs during processing. Following photography, the item can be either
powdered or placed in a cyanoacrylate chamber. A positive control, generally a
, ﬁngerprint placed on a piece of acetate backer, is placed in the chamber with the
questioned item to ensure the procedure is working. If any ﬁngerprints are visible

following fuming, they are photographed. If prints are not visible as a result of fuming,

10

ﬁngerprint powder can be applied for enhancement (which may occur in crime
laboratories with smaller budgets and less ﬁngerprint sophistication and technology) or
ﬂuorescent dyes can be applied to eliminate the background distraction. In some
instances the addition of powder at this step results in lost latent print detail, with the
print becoming engulfed in the powder and minutiae are no longer visible. When this
occurs, it is the last step for processing; the latent print has been lost within the black
powder, and perhaps only the pattern type and any photographs that have been taken are
of value for identiﬁcation.
Difﬁcult Substrates for Powdering

Wood, leather, cardboard, metals and in particular items made of plastic can be
difﬁcult for processing and capturing enhanced latent prints. Porous materials are
problematic because of their nature to absorb moisture, while the non-porous materials
can become engulfed in the black powder, making the latent print no longer visible.
Plastic materials can exhibit this same problem with the entire backgrOund becoming
black, resulting in a print that is indistinguishable and has few visible ridges, as the
powder not only adheres to the print but the background as well. There are four results
that can occur as a result of the reaction between the powder and plastic. First, the latent
print may become enhanced, which produces visible minutiae for identiﬁcation. Second,
the powder can adhere to all of the ridges, but at times also ﬁll some of the furrows,
causing the ridges and minutiae to become difﬁcult to distinguish and identify. Third, the
powder can ﬁll most of the furrows, leaving few ridges and identiﬁcation points visible.
Finally, the area becomes engulfed, with powder adhering to ridges, furrows and

background plastic, allowing only a few or no ridges or minutiae to be visible.

ll

The chemical makeup of a plastic item may inﬂuence how a fingerprint adheres to
it and therefore the success of subsequent processing. Plastics have properties that are
chosen and altered to meet a range of applications. The type of plastic encountered can be
deduced from its Plastic Identiﬁcation Number or Resin Identiﬁcation Code (Table l),
which is placed on the bottom of the item. This code was developed in 1988 by The
Society of the Plastics Industry to give manufacturers a uniform convention for labeling
the different types of materials and also provides a label to distinguish plastics and their
chemical components for recycling (The Society of Plastics Industry).

Table 1 Plastic Identification Table

 

 

 

 

 

 

 

 

 

 

 

 

Plastic Material Surface Sample Materials
Identiﬁcation Composition Tension
Number (dynes/cm)
Poly(ethylene 43 " Soda bottles, water bottles, medicine containers,
P terephthalate) lotion bottles.
High-density 33 Containers (laundry/dish detergent, fabric
£35 polyethylene softeners, bleach, milk, pill bottles, butter,
HOPE shampoo, conditioner, and cleaning supplies)
grocery bags
Poly(vinyl 39.40 Pipes, shower curtains, cooking oil bottles, shrink
& chloride) wrap, clear medical tubing, vinyl dashboards and
seat covers, coffee containers, medical
V containers.
& Low-density 31 Wrapping ﬁlms, grocery bags, sandwich bags.
1 eth lene
__ka P0 y Y
Polypropylene 29 Tupperware®, syrup bottles, yogurt tubs, cd
spindles.
3p
Polystyrene 33 Coffee cups, meat trays, packing peanuts,
Styrofoam insulation, beverage lids.
Pi
“Other” These materials can be made of any combination
of plastic identiﬁcation #1-6.
OTHER

 

Plastic identification numbers with their respective chemical names along with surface
tension values for the untreated plastic and example materials for each plastic type.
Surface tensions obtained from Flexocon. ‘Other’ indicates a chemical makeup of any
combination of resins #1-6.

Manufacturers modify the behavior of the plastic depending on the interaction

that is required between the item and internal or external sources. These modifications

 

typically come in the form of additives which diffuse within the polymer, and tend to
migrate toward the surface. Additives include antiblocking agents which reduce the
polymer’s tendency to stick to an adjacent polymer (e. g. synthetic and natural silicas, as
well as minerals), slip agents (e. g. oleic acid for polyethylene and erucamide for
polypropylene), antislip agents (e. g. ethylene/maleic anhydride copolymers), lubricants
(e. g. fatty-acid esters and amides, polyethylene waxes and silicones) and mold release
agents. Antifogging agents keep the material transparent and increase the surface tension
of the polymer. Additional additives include antistatic agents (e.g. alkyl phosphonium
and alkyl sulfonium salts), ﬁllers and reinforcements, antimicrobials or biocides (e. g. 2-n-
octyl—4 isothiazolin-3 and copper-8-quinoleate), desiccants (e. g. ethylene vinyl alcohol)
and fragrance enhancers. Plasticizers are another additive type, that increases the
polymer’s ﬂexibility, workability, and extensibility, and modify the polymer’s ratio of
polar to non-polar groups depending on the plasticizer’s application. Common
plasticizers include diethylhexyl phthalate and di(2-ethylhexyl) adipate'(DEA) combined
with epoxidized soybeam (Hernandez et al. 2000).

Some plastic items may have a surface treatment applied to improve barrier
properties, or to enhance a plastic’s ability to retain inked printing or adhesives. To
improve the bonding of inks and adhesives (e. g. labels), treatments that supply polar
groups which provide stronger secondary bonding are used, ultimately increasing the
surface energy of the material. Other manipulations include ﬂame treatments, corona
discharge treatments, and ozone treatments, which all increase adherence of inks and
adhesives by promoting oxidation at the surface (Hernandez et al. 2000). Some plastic

types, such as polystyrene, are modiﬁed to absorb proteins, which could include the

13

protein left behind from a ﬁngerprint. Such characteristics could increase a plastic’s
tendency to hold/lose a latent print more so than another plastic type (Seradyn 1999).
Characterization of Fingerprint Adhesion to Plastics
Surface Tension Analysis

There are a number of factors that alter the surface tension of plastic materials,
typically measured in dynes/cm, affecting their ability to retain inks, labels, and glues,
which also could conceivably inﬂuence the adhesion of ﬁngerprints. These include the
plastic composition, additives, and surface treatments (Hernandez et al. 2000). To
measure surface tension, calibrated liquids may be applied. If the surface energy of the
liquid is greater than the substrate, the liquid will “wet out” or spread over the surface.
When the surface energy of the liquid is less than the substrate, the liquid will “bead up”
or shrink to a thin line. The surface energy of the liquid that closely relates to that of the
substrate results in the liquid holding for one to three seconds before “de-wetting”
(ACCU DYNE TEST Diversiﬁed Enterprises). Materials that have been coated with the
same surface treatment but are chemically different may exhibit different surface tensions
(Van Iseghem).
Microscopic Characteristics of Fingerprints

The Scanning Electron Microscope (SEM), introduced in 1965, has proven to be
very useful to the scientiﬁc community due to its large depth of ﬁeld allowing more of
the sample to be in focus at one time. In addition, the SEM is also useful for its wide
range of magniﬁcation and simple sample preparation techniques. The SEM is designed
to send a beam of electrons that strike the surface of a sample resulting in interactions

which produce secondary products such as secondary electrons, X-rays, heat and light.

14

The secondary electrons produce the image of the sample G’legler et al. 1993). An SEM
can be used to examine sample topography by producing a magniﬁed image of the item.
This technique aids forensic analysis of items such as metal fragments or paint. The SEM
also has the ability to examine morphology, displaying the shapes and sizes of the
particles that make up the sample. Typically the SEM in forensic science has been used to
visualize shell casings, shot from shotgun shells, and those items mentioned above, but it
is also possible to look at ﬁne details in ﬁngerprints.
Scanning Electron Microscopy — Energy Dispersive X -Ray Spectrometry

The SEM equipped with an Energy Dispersive X-Ray Spectrometer (EDS) can be
used to obtain an elemental analysis of a sample by detecting the emitted X-rays of many
organic and inorganic Samples depending on coatings and atomic weight of the elements
analyzed. These X-rays have an energy that is characteristic to parent elements, allowing
the SEM-EDS to generate a qualitative and quantitative elemental proﬁle. Sample
preparation for SEM-EDS is simple for non-biological samples: the samme is placed on
an aluminum stub with adhesive tabs, double-sided tape, rubber cement or carbon tape.
Sample preparation is the same for biological samples once it has been critically point
dried, which removes water while preserving morphological features. If the sample is not
conductive, it must be coated, typically with carbon, to achieve a signal strong enough for
the detector to measure (Saferstein 1988). SEM-EDS can be used in forensic analysis to
determine the composition of a sample by identifying the elements and compounds

present (e. g. soil samples).

15

Proﬁlometry

A proﬁlometer can be used to measure surface texture by dragging a stylus across
the surface of the sample. It measures the step heights along the sample (the differences
between the high points and low points) which provides data for calculating the surface
roughness. This is done by a graph output of step height versus position (Stanford
Nanofabrication Facility). Typical limits in sample thickness are 10mm with a horizontal
diameter limit of 125mm.
Background on the Research Presented Here

The research detailed below originated from observations made by Lieutenant
Kathy Boyer, a latent print supervisor in the Bridgeport Laboratory of the Michigan State
Police. Lieutenant Boyer processed a box containing a label by cyanoacrylate fuming.
When applying black powder to the label however, it became engulfed and the palm print
was barely visible. To develop latent prints on the box, Lieutenant Boyer applied the
ninhydrin hexane solution, described by Scarborough (2001), with a foam brush across
the box and unintentionally wiped it across the label. The black powder was rinsed from
the label, and the palm print became visible and identiﬁable. This rinsing also developed
a new print that was previously not visible or developed. Lieutenant Boyer attempted this
rinsing on other semi—porous and non-porous items, where successful enhancement
occurred on magazines, photographs and plastic items.
Research Goals

The research project described below was designed to determine what plastic
types (such as poly(ethylene terephthalate), polypropylene, etc.) would beneﬁt from this

rinsing technique through the examination of physical (plastic color, surface roughness,

l6

and surface tension) and chemical characteristics (plastic type, presence or
absence/removal of inked printing and/or labels) in order to identify what properties of
the plastic items resulted in successfully or unsuccessfully enhanced results. The research
was also designed to analyze the effects of different cyanoacrylate chambers and inter-
individual variability effects on rinsing results, as well as rinsing solution compositions to
determine the optimal solution makeup.

To achieve these goals, over 100 plastic containers and bags, each with a plastic
identiﬁcation number, were processed. Surface tension values were obtained for items to
determine if there was a correlation between these values and the processing results. A
SEM was used to visually identify locations where the black powder was adhering, and to
determine when and ‘where changes in the amounts of cyanoacrylate and powder
occurred. Examination of elemental changes in the cyanoacrylate, powder, and ninhydrin
hexane solution during the procedure was attempted using SEM-EDS. Lastly, a
proﬁlometer was used to examine the surface texture of the plastic items to determine if
there was a correlation between the texture and successful or unsuccessful results. The
surface roughness was evaluated on items that had at least one successfully and one

unsuccessfully rinsed print.

Materials and Methods

Sample Collection
Plastic household items were donated by individuals and collected. Items had

plastic identiﬁcation numbers and were of various composition, uses, sizes, colors, and

17

surface textures. Some items had labels and/or inked printing while others had neither.
APPENDIX A details these items.
Rinsing Solution

A ninhydrin hexane solution (Scarborough 2001) was prepared by adding
approximately 5 grams (+/- 0.05 g) of Ninhydrin to a 50 mL beaker along with 10 mL of
methanol. The solution was mixed on a stir-plate using a stir-bar for 10 minutes and then
poured into a 1 L brown bottle, to which 200 mL of ethyl acetate and 790 mL of hexane
were added and stirred for an additional 10 minutes. The solution was tested each time by
placing a few ﬁngerprints on white test paper, to which the solution was applied by
submersion. The paper was then placed into an oven at 120° F with hot water in a beaker
for 10 minutes. A positive result was demonstrated by the presence of a purple print.
Sample Processing

Fingerprints were placed on the plastic items by wiping a thumb across the face to
ensure that each latent print contained adequate sweat and oil, and touching the items.
The ﬁngerprints were circled with a black permanent marker and labeled. Notations were
made if the ﬁngerprint had been placed on top of inked printing, if an adhesive label had
been removed, and if the ﬁngerprint had been placed fully on or half on/half off of the
removed label location.

The items were then placed in a Fisher Hamilton cyanoacrylate chamber along
with an acetate backer containing a latent print to ensure that the chamber was working
properly. The hot water tap was run for 30 seconds, and 150 mL of hot water was placed

in a beaker, which was put in the chamber. Enough cyanoacrylate was placed in a small

18

tray to cover the bottom and was heated using a heating element in the chamber, allowed
to vaporize for 20 minutes, then allowed to vent for 10 minutes.

Eight items were also fumed in a Mason Vactron, MVC 5000 cyanoacrylate
chamber and processed to ensure that the results were not affected by different
cyanoacrylate fuming conditions. All plastic items were then processed with a ﬁberglass
brush and Carbon Black powder from Lightning Powder Company, Inc. by swirling the
brush across the surface for 5 — 10 seconds, followed by print photography.

The rinse solution was applied to the fumed and powdered prints using a foam
brush with mild pressure, by wiping across the sample until the excess black powder had
been removed (as many as ﬁve or six times depending on the plastic item). The print was
allowed to dry for 10 minutes and photographed. Initially, the brush was oversaturated
with solution before applying it to the item, but as the technique developed, the solution
was allowed to drain from the brush until there was enough to just wet the brush.
Following photography, the item was processed with black powder for a second time,
followed by a second rinse. This cycle of events, powdering/rinsing, continued until one
of seven events occurred: the latent print became identiﬁable or enhanced, the latent print
had areas that were enhanced but also areas where ridges and minutiae were removed, the
latent print lost detail when the ridges or minutiae wiped off, the latent print lost detail
when ridges blurred together, the latent print wiped from the surface leaving a black
surrounding background, the latent print became further engulfed in the black powder, or
the print remained but black powder would not adhere.

To ensure that inter-individual variability did not affect rinsing results, 21 latent

ﬁngerprints from 10 items, ﬁve prints on zip close bags and 16 prints on Kroger grocery

l9

bags, were collected. These items were laid on a table and handled by anonymous donors,
and processed.
Rinse Solution Analysis

Variations in the chemical composition and ratios of the rinse solution were tested
to determine if there was an optimal composition for the rinse, as well as if heptane or
hexane was more effective (Table 2). The original quantity of ninhydrin hexane solution
was cut by 1/5 for the ﬁrst seven solutions to reduce waste. In addition, an eighth
ninhydrin solution (W ertheim), developed to reduce the running of inks on porous
surfaces, was made and tested.

Table 2 Rinsing Solution Chemicals

 

 

 

 

 

 

 

 

 

 

Solution N inhydrin Methanol Ethyl Acetate Hexane/Heptane Other (mL)
Number (grams) (mL) (mL) (mL)

1 0 2 40 158-Heptane

2 1 0 40 160-Hexane

3 l 2 0 l98-Hexane

4 1 2 40 158-Heptane

5 1 2 0 198-Heptane

6 0 0 40 l60-Hexane

7 l 2 40 0

8 1 lS-EtOH 5 200-Heptane 3/5-Acetic Acid

 

 

 

 

 

 

 

Quantities of ninhydrin, methanol, ethyl acetate and hexane/heptane in the various wash
solutions are shown. Solution eight came from Wertheim and is composed of ethanol
(EtOH) and acetic acid in addition to the other chemicals.

Each solution with ninhydrin and methanol was stirred for 10 minutes in a 10 mL
beaker to dissolve the ninhydrin and then combined with the remaining components in a
250 mL ﬂask and mixed for 10 minutes on a stir-plate with stir-bar. If the solution
contained ninhydrin but not methanol, the ninhydrin was combined with ethyl acetate and
heptane/hexane in a 250 mL ﬂask and stirred for an additional 10 minutes. The eighth

solution was made by mixing the ninhydrin, ethanol, acetic acid, and ethyl acetate for 10

minutes in a 50 mL beaker and then combined with heptane in a 250 mL ﬂask and stirred

2O

for another 10 minutes. Each solution was used to process a white, #2 high—density
polyethylene Kroger grocery bag with two latent ﬁngerprints present.
Instrumental Techniques
Surface Tension Determination

AC C U DYNE TEST Marker Pens, accurate to +/- 2.0 dyne/cm, were used to
measure the surface tension of the plastic items. Preliminary tests showed that surface
tension readings were unchanged at different stages of the processing cycle, i.e., prior to
cyanoacrylate fuming, after cyanoacrylate fuming, after powdering, or after rinsing, thus,
the readings were taken after the ﬁngerprints were marked and the item had been
cyanoacrylate fumed. The surface tension was measured near each ﬁngerprint by
choosing a surface tension pen and drawing it across the surface three times and
evaluating the ink swath’s reaction to the material. If the line of ink beaded up, the next
lower surface tension pen was examined. If the line of ink remained “wetted out” on the
surface for more than two seconds, the next higher surface tension pen was then
examined. If the ink swath held for one to three seconds, that surface tension was
recorded.
Scanning Electron Microscopy

A ISM-6400 Scanning Electron Microscope was used with the AnalySIS
computer program to produce digital images of ﬁngerprints at various stages of the
powdering/rinsing cycle. An accelerating voltage of 20kV and a working distance of
39mm were chosen with a magniﬁcation of 10 to 13X. Four ﬁngerprint samples were laid
on a white #2 Kroger grocery bag, cyanoacrylate fumed and processed to various stages.

Table 3 displays the ﬁngerprint samples that were analyzed. Samples were coated with

21

gold for two minutes using an Emscope Sputter Coater, SC 500. Images included ridges

only, furrows only, and an overall view of the ﬁngerprint.

 

 

 

 

 

 

Table 3 Sampling Stages
Sample Number Latent Print Processing
1 Cyanoacrylate fumed only.
2 Cyanoacrylate fumed and powdered.
3 Cyanoacrylate fumed, powdered, and rinsed once.
4 Cyanoacrylate fumed, powdered, and rinsed three times.

 

 

 

The sample numbers with the amount of processing that the sample had undergone are
displayed.

A second set of images was taken of a single latent ﬁngerprint at various stages of
the powder/rinsing cycle as described in Table 3. At each stage, the print was coated with
gold for two minutes using an Emscope Sputter Coater, SC 500. SEM parameters
remained the same however, a magniﬁcation of 20X was used.

Scanning Electron Microscopy — Energy Dispersive X Ray Spectrometry

SEM-EDS with a Vantage 1.5.1, Therrno Electron computer program was used to
examine chemical changes that may be occurring to the ﬁngerprint and processing
chemicals during the procedure. Two sample sets were collected as described in Table 3.
One sample set was carbon coated using an EFFA MkII Carbon Coater No. 12560. An
SEM accelerating voltage of 20kV was chosen with a working distance of 8mm and a
magniﬁcation of 2300X. The condenser lens setting was a course focus of 8 and a ﬁne
focus of 60 in order to achieve a strong enough signal to detect. Carbon elemental
information was collected as well as titanium, calcium, magnesium, aluminum, etc.
Proﬁlometry

Eight plastic items previously processed were examined using a Dektak IIA
proﬁlometer. These items were chosen based on two variables. First, the sample needed

at least one successfully rinsed print and at least one unsuccessful result. Comparing

22

surface texture results for prints on the same container yielded a correlation between
texture values and successful responses. The second variable dealt with limitations in the
proﬁlometer itself, for which the tested material must be thin (less than 10mm) and
perfectly ﬂat. A small section, approximately 1 inch by 1%: inch, near each ﬁngerprint was
cut from the plastic using a razor blade, taped horizontal to the stage, and read using low
speed over 8mm of sample. Each sample was scanned three times and each scan

generated an average height to give a surface texture measurement.

Results

Rinsing Technique Evaluation

After processing the 102 plastic items and nearly 300 ﬁngerprints, it appeared that
there were seven common results following the powdering/rinsing procedure (Table 4).
The rate of ﬁngerprint enhancement, where a success was a print that was either
enhanced or enhanced but lost detail, was 53.1%. Outcomes included Enhanced Print
“EP” (print became enhanced with minutiae details visible), Enhanced Print/Lost Detail
“EP/LD” (print had areas where it was enhanced and areas where minutiae were lost),
Lost Print/Detail “LP/D” (areas of print wiped off resulting in the loss of minutiae), Lost
Print/Blurred “LP/B” (minutiae were lost by ridges blending together), Lost
Print/Background Black Powder Surrounding “LP/BP” (a majority of print wiped away
with background black powder adhering to surroundings leaving a nearly clean outline of
the print) , Black Powder Engulfed “BP” (print and background became engulfed with

powder and minutiae were not visible), and Print Remains/No Black Powder Remaining

23

“PR/NBP” (print remained and could be seen obliquely however, no black powder was
adhering to ridges or background).

Table 4 Processing Results

 

 

Rinsing EP EP/LD LP/D LP/B LP/BP BP PR/NBP
Result '

Number of 83 72 52 25 6 44 10
Occurrences

 

 

 

 

 

 

 

 

 

 

The number of times that each processing result occurred is shown. EP-Enhanced Print,
EP/LD-Enhanced Print/Lost Detail, LP/D-Lost Print/Detail, LP/B-Lost Print/Blurred,
LP/BP-Lost Print/Background Black Powdered, BP-Black Powder Engulfed, PR/NBP-
Print Remains/No Black Powder Present

The entire processing results for each print can be found in APPENDD( A along
with the items’ plastic identiﬁcation number, color, visible surface ﬁnish, and surface
tension measurements. The most frequent result (28.4%) was print enhancement
following the powder/rinse procedure, “EP” (Figures 3 — 9). This occurred when most of

the background black powder rinsed clean from between the ridges and surrounding areas

making the ridges distinct and the print identiﬁable.

24

Fi ure 3 Enhanced Print on Sam Ie #96-a

 

 

a b

A ﬁngerprint left on sample #96-a, Minute Maid OJ Container, that was processed with
black powder after being cyanoacrylate fumed (a), and after three rinsing cycles (b). The
minutiae have been enhanced and individual ridges are present in the rinsed image.

Fi

ure 4 Enhanced Print on Sam le #79

a b

A ﬁngerprint left on sample #79, Lid from Chlorox2 Container, that was processed with
black powder after having been cyanoacrylate fumed (a) and after three rinsing cycles
(b). In the powdered image only a few ridges are visible, but after the rinsing, the ridges
and minutiae are observable.

25

Fi ure 5 Enhanced Print on Sam le #78

    
 
 

  
  

 

a ' 7 ' b

A ﬁngerprint left on sample #78-a, Chlorox2 Bleach Container, that was processed with
black powder after having been cyanoacrylate fumed (a) and after three rinsing cycles
(b). In the powdered image only a few ridges are visible, but after the rinses, the ridges
and minutiae are observable.

re 6 Enhanced urint on sam . le #45-b

 
     

  

. a " -- ' A b
A ﬁngerprint left on sample #45-b, Paul Mitchell Shampoo Container, that was processed
with black powder after having been cyanoacrylate fumed (a) and after three rinsing
cycles (b). The ﬁngerprint ridges are very blurred in the powdered image whereas in the
rinsed image minutiae points are visible and identiﬁable.

Fi

   

ure 7 Enhanced Print on Sam . le #32-a

     

- a .:-.:. : ’ . , ; ' b

A ﬁngerprint left on sample #32-a, Kroger Half and Half Container, that was processed
with black powder and cyanoacrylate fumed (a) and after three rinsing cycles (b). The
black powdered image appeared to have reversed ridges that were blurred while the
rinsed print had distinct ridges and identiﬁable minutiae. Note that a label had been
removed prior to placing the latent print on the surface.

26

  

  

b

‘ . ‘ a
A ﬁngerprint left on sample #32-b, Kroger Half and Half Container, that was processed
with black powder after having been cyanoacrylate fumed (a) and after three rinsing
cycles (b). The black powdered image appeared to have reversed ridges that were blurred
while the rinsed print had distinct ridges and identiﬁable minutiae.

b
essed
with black powder and cyanoacrylate fumed (a) and after three rinsing. cycles (b). The
black powdered image appeared to have reversed ridges that were blurred while the
rinsed print had distinct ridges and minutiae.

 

The next most frequent result (24.7%) was a print that was enhanced but lost
detail, “EP/LD” (Figures 10 — 13). These latent prints had areas that were enhanced and
areas where minutiae were lost either through the ridges blurring together or wiping off

and losing minutiae.

27

Fi re 10 Enhanced Print/Lost Detail on Sam-1e #11-

   
 

   
  

a m b
A ﬁngerprint left on sample #11-c, Small Pill Bottle, that was processed with black
powder after having been cyanoacrylate fumed (a) and after six rinsing cycles (b). The
ridges became more distinct near the perimeter, but the print began to lose detail near the
core. Note the white square-shaped area on the left side of (b) where a label had been
removed prior to leaving the print and processing.

.1; w .
, a: . agw,...*r.».:em. ~ . , -' . .
. ‘i‘ — .m‘r‘ ' '4 a b
A ﬁngerprint left on sample #101-a, Clairol Hair Conditioning Container, that was
processed with black powder after having been cyanoacrylate fumed (a) and after ﬁve
rinsing cycles (b). The ﬁngerprint was enhanced near the perimeter and lost detail near
the core.

   

y ,

28

Fi re 12 Enhanced Print/Lost Detail on Sample #87-a

      

a b

A ﬁngerprint left on sample #87-a, Joy Dish Soap Container, that was processed with
black powder after having been cyanoacrylate fumedla) and after three rinsing cycles
(b). The print was enhanced near the tip and core where it had been over glued with the
fuming and lost detail below the tip.

Fi-

    
 

re 13 Enhanced Print/Lost Detail on Sam le #95-c

   

a b

A ﬁngerprint left on sample #95—c, Tropicana OJ Container, that was processed with
black powder after having been cyanoacrylate fumed (a) and after one rinsing cycle (b).
The ﬁngerprint was enhanced near the perimeter and away from the core and lost detail
near the core and surrounding ridges.

The third most frequent result (17.8%) was when the entire print was lost or a

majority of the ridges were removed and minutiae were lost, “LP/D” (Figures 14 — 15).

29

These results occurred when most of the latent print wiped clean, leaving very few visible
ridges or when a majority of the minutiae, previously visible, wiped away.

Ie #28-c

    
   

Fi ure 14 Lost Print/Detail on Sam

  
   

. . 215a b

A ﬁngerprint left on sample #28-c, Daily Defense Container, that was processed with
black powder after having been cyanoacrylate fumed (a) and after four rinsing ‘cycles (b).
The latent print had lost a majority of the minutiae that were present in the powdered
print. The surrounding background became darkened by the powder.

Fi

   
  

ure 15 Lost Print/Detail on Sam n le #69-b

  

A ﬁngerprint left on sample #69-b, Fresh Cut Lettuce Bag, that was processed with black

powder after having been cyanoacrylate fumed (a) and after three rinsing cycles (b). The

latent print had lost a majority of the minutiae that were present in the powdered print.
The fourth most frequent result (15.1%) was when the print became engulfed in

black powder, “BP” (Figures 16 — 18). This occurred when the black powder adhered to

30

not only the latent print, but also the surrounding background making it indistinguishable
and resulting in the absence of visible ridges.
III;

re 16 Black Powdered on Sam . le #74-a

   
 

    
 

 

f

a . . , , . ,
A ﬁngerprint left on sample #74-a, Humidiﬁer Bacteriostat, that was processed with
black powder after having been cyanoacrylate fumed (a) and after three rinsing cycles
(b). The print became engulfed in the black powder and no distinction could be made
between the ﬁngerprint and the surrounding area. No ridges were visible in the rinsed
print.

Ie #33-a

Fi - ure 17 Black Powdered on Sam
. . 2 " rréi 9‘1

airy V

    
 

   

   

  

. p _ a ‘
A ﬁngerprint left on sample #33-a, Kroger Toilet Bowl Cleaner, that was processed with
black powder after having been cyanoacrylate fumed (a) and after ﬁve rinsing cycles (b).
The print had become engulfed in black powder and ridge detail was indistinguishable.

31

 

A ﬁngerprint left on 3
powder after having been cyanoacrylate fumed (a) and after four rinsing cycles (b). The
print became engulfed in the black powder and minutiae could not be identiﬁed.

The ﬁfth most frequent result (8.6%) was when the latent print was lost or became
blurred, “LP/B” (Figure 19). On these black powder either remained in the furrows of the
print or the ridges came together and were indistinguishable as a result of the rinsing

process. Few, if any, minutiae were visible.

          

 
 

‘ " a; .
5 ‘1" l .«o

A ﬁngerprint left on sample #62-a, Meijer Grocery Bag, that was processed with black
powder after having been cyanoacrylate fumed (a) and after three rinsing cycles (b). The
rinsed print had become blurred where the ridges blended together in the area
surrounding the core and minutiae were lost.

32

The sixth most frequent result (3.4%) was a print that remained, but no black
powder was present, “PR/NBP” (Figure 20). This occurred when no black powder
adhered to the latent print or the surroundings, but the latent print was still present and
could be seen through oblique lighting.

‘- re 20 Print Remainin_ 0 Black Powder Surroundin on Sample #102-b

     

A fingerprint left on sample #102-b, Dannon Yogurt Container-Large, that was processed
with black powder after having been cyanoacrylate fumed (a) and after three rinsing
cycles (b). The print retained the minutiae, but the black powder would not adhere to the
ridges to further enhance the print. The black powder did not adhere to the background
either except in a few areas. The print could be seen if held at an oblique angle.

The least frequent result (2.1%) was a latent print that was lost and the
surrounding background was black powdered, “LP/BP” (Figures 21 - 22). This result

occurred when a majority of the latent print wiped from the plastic material leaving

the print area free of powder with the only black powder present surrounded the area.

33

    

a b

A ﬁngerprint left on sample #13-e, Large Twist Cap Bottle, that was processed with
black powder after having been cyanoacrylate fumed (a) and after three rinsing cycles
(b). A majority of the print disappeared leaving a white area in its place and the
surrounding plastic material was covered in black powder.

Fi

   

   
  
   

re 22 Lost Print/Black Powder Surroundin on Sam - le #15-c

~ -~ a 1‘ A. b
A ﬁngerprint left on sample #15-c, Yoplait Yogurt Cup-Strawberry, that was processed
with black powder after having been cyanoacrylate fumed (a) and after three rinsing
cycles (b). The print lost all detail and black powder covered the surrounding area.
Processing Identifiable Prints

There were 19 plastic items and 30 ﬁngerprints that when ﬁrst processed with

black powder, did not require further enhancement. Although these ﬁngerprints were

identiﬁable after being powdered, they were processed with the rinsing solution

34

nonetheless (T able 5). Sixteen of the ﬁngerprints became further enhanced by this

process (53.3%), while the remaining results were “LP/D”, “LP/B” or “BP”.

Table 5 Initially Identifiable Latent Prints

 

Item

Fingerprint Number

Processing Result

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12-Laundry Detergent Bottle (Xtra) 12-c EP/LD
l3-Large Twist Cap Bottle 13-a EP/LD
l3-b EP/LD
13—c EP/LD
l3—d LP/B
15-Yoplait Yogurt Cup (Strawberry) 15-a LP/D
l6-Yoplait Yogurt Cup (Cherry) 16-b LP/D
16-c LP/D
17-Dannon Yogurt Cup 17-a LP/D
21-Vita Tabs Bottle 21-a EP/LD
22-Sprite Bottle 22-a EP/LD
22-b EP/LD
22-c LP/D
. 22-d LP/D
23-Alcon Bottle 23-b LP/D
23-c EP/LD
23-d EP/LD
27-Appearance Body Wash Container 27-a EP
4l-Intemational Delight Creamer Container 41-b EP/LD
60-Target Bag 60-h LP/B
62-Meijer Grocery Bag 62-b EP/LD
64-Dollar General Bag 64-a EP/LD
64-b BP
67-Ear Care Container 67-a EP/LD
67-b EP/LD
69-Fresh Cut Lettuce Bag 69-b LP/D
70—Blue Container 70—a EP
82-CD Holder Base 82-b BP
83-CD Holder Base 83-b EP/LD
87-Joy Dish Soap Container 87-a EP/LD

 

Sample containers with an identiﬁable print prior to rinsing are detailed, along with the
overall processing result. EP-Enhanced Print, EP/LD-Enhanced Print/Lost Detail, LP/D-
Lost Print/Detail, LP/B-Lost Print-Blurred, LP/BP-Lost Print/Background Black
Powdered, BP-Black Powder Engulfed, PR/NBP-Print Remains-No Black Powder

Present.

35

 

Effect of Plastic Variables on Fingerprint Enhancement

To better understand the relationships between the plastic variables, including
plastic type, color, surface ﬁnish, inked printing/adhesives, and surface tension, data for
each were placed on a Microsoft Excel spreadsheet (APPENDIX A), sorted, and
compared to the processing results.
Plastic Types

The plastic types collected (APPENDD( A) were compared to their ﬁngerprint
enhancement success rates (Table 6). The #7 and #3 produced the highest enhancement
success rates (60% each), although they had small sample sizes. Of the large sample sizes
(40 or more ﬁngerprints) #2 produced the highest success rate (50.6%) with #5 having
nearly the same success (48.8%). Remaining success rates were in the low 40% range.
Plastic types #1 and #7 lost prints at a higher rate followed by 5 and 3. Large sample
sizes tended to have a higher percentage of lost prints. Plastic #4 and #6 were more likely
to produce engulfed prints. Plastic #3 never lost a print however, 40% of the time the
rinsing technique could not enhance the print and black powder would not adhere.

Table 6 Plastic Type Enhancement Success Rates

 

 

 

 

 

 

 

 

 

Plastic Number of Percent Percent Percent Percent “PR/NBP”
Type Fingerprints Successes Lost Print “BP”
1 41 43.9 46.3 9.8 0
2 170 50.6 25.9 14.1 11.8
3 5 60.0 0.00 0 40.0
4 10 40.0 10.0 40.0 10.0
5 43 48.8 30.2 11.6 9.3
6 20 45.0 15.0 35.0 5
7 5 60.0 40.0 0 0

 

 

 

 

 

 

 

Plastic types with the number of ﬁngerprints processed on each are displayed. The
success rates are included for each plastic type, deﬁned as a print that was either
enhanced or enhanced but lost detail. The percent lost print includes those where the print
was either uninformative through loss of details, blurring, or only background powder
remaining. BP-Black powder engulfed, PR/NBP-Print remains/no black powder
adhering.

36

Plastic Color

There were 11 different colors of plastic items that were processed, generating a

range of results (APPENDIX A). Table 9 displays the different colors represented, the

number of ﬁngerprints that were processed within each color category, and the percent of

successful enhancements. The three orange ﬁngerprints were all enhanced, although they

were least represented (2 items). Fingerprints on white materials, with the larger sample

size (39 items), exhibited the lowest success rate (49.6%). Enhancement rates on other

colors ranged from 71.4% for red to 50% for blue, cream, green, and yellow. Cream

colored items lost prints most frequently (50%) while orange, pink and red, never lost

prints. Pink and yellow tended to have latent prints that became engulfed by the black

 

 

 

 

 

 

 

 

 

 

 

 

 

powder.
Table 7 Color Analysis
Color Number of Percent Percent Percent Percent
Fingerprints Successes Lost Print “BP” “PR/NBP”
Blue 12 50.0 16.7 16.7 16.7
Brown 10 60.0 10.0 _ 20.0 10.0
Clear 93 52.7 31.2 12.9 3.2
Cream 14 50.0 50.0 0 0
Gray 13 69.2 7.7 15.4 7.7
Green 8 50.0 25.0 12.5 12.5
Oragge 3 100 0 0 0
Pink 3 66.7 0 33.3 0
Red 7 71.4 0 28.6 0
White 123 49.6 32.5 16.3 1.6
Yellow 6 50.0 16.7 33.3 0

 

 

 

 

 

 

Plastic colors with the number of ﬁngerprints processed. The success rates are included
for each color, deﬁned as a print that was either enhanced or enhanced but lost detail. The
percent lost print includes those where the print was either uninformative through loss of
details, blurring, or only background powder remaining. BP—Black powder engulfed,
PR/NBP—Print remains/no black powder adhering.

37

 

Surface Finish

Plastic items were given a surface ﬁnish description based on the appearance and
texture (APPENDIX A). The four categories included “glossy”, which had a very
smooth, shiny surface, “smooth” which had a ﬂat surface, “textured” which had a mildly
rough surface, and “rough textured” which had large pits on the surface. While all ﬁnish
types had a greater success rate compared to losing the print, the rough textured items had
the greatest success (67.5%) while glossy ﬁnished items and had the least (45.2%). The
reverse order occurred for losing prints with glossy items occurring more frequently
(40.9%) than rough textured items (10.0%). The percent of “BP” and “PR/NBP” for each
ﬁnish were similar for all ﬁnishes, <18% and <8%, respectively.

Table 8 Surface Finish Analysis

 

 

 

 

 

 

Surface Number of Percent Percent Percent Percent

Finish Fingerprints Successes Lost Print “BP” “PR/NBP”
Glossy 93 45.2 40.9 1 1.8 2.2
Smooth 118 50.9 18.6 17.0 4.2
Textured 41 63.4 19.5 17.1 0
Rough 40 67.5 10.0 15.0 7.5
Textured

 

 

 

 

 

 

Surface ﬁnish with the number of ﬁngerprints processed. The success rates are included
with a success being a print that was either enhanced or enhanced but lost detail. The
percent lost print includes those where the print was either uninformative through loss of
details, blurring, or only background powder remaining. BP-Black powder engulfed,
PR/NBP-Print remains/no black powder adhering.

Inked Printing and Adhesive Analysis

Surface treatments are applied to plastic items in order to increase the plastic’s

ability to retain inked printing and adhesives (labels) (APPENDD( A). The effect of these

modiﬁcations on the ﬁngerprint processing varied (Table 9). A notation was made as to

whether there was inked printing present in the location of the latent print and whether an

adhesive label had been removed where the latent print was deposited. The presence or

38

 

removal of a label resulted in just over 50% successfully enhanced prints, while the

presence of inked printing resulted in a greater number of lost prints (48.4%) than

successful rinses (35.5%). There were instances where prints that were placed where a

label had been were enhanced and instances where they were lost. No predictions could

be made as to whether a certain result type would occur. Given an adequate sample size,

it appears that ink impacts the processing result.

Table 9 Inked Printing/Adhesive Analysis

 

 

 

 

 

Surface Number of Percent Percent Percent Percent
Modiﬁcation Fingerprints Successes Lost Print “BP” “PR/NBP”
Inked 31 35.5 48.4 9.7 6.5
Printing
Label 55 54.5 30.9 14.5 0.0
No Label 206 55.3 24.8 16.0 3.9

 

 

 

 

 

 

 

Surface modiﬁcation with the number of ﬁngerprints processed. The success rates are
included for each modiﬁcation with a success being a print that was either enhanced or
enhanced but lost detail. The percent lost print includes those where the print was either
uninformative through loss of details, blurring, or only background powder remaining.
BP-Black powder engulfed, PR/NBP—Print remains/no black powder adhering.
Surface Tension

Surface tension readings were taken for each item (APPENDD( A). Table 10
displays the range in readings for each plastic identiﬁcation number category in addition
to their literature values. Overall, higher success rates occurred with the higher surface
tension readings. The highest success rate (70.6%) happened with a surface tension
reading of 36 dynes/cm whereas a surface tension reading of less than 30 dynes/cm had
the lowest success rate (20.0%). The remaining readings were near 60% while a reading
of 32 dynes/cm had a success rate of 48.9%.

A comparison of experimental surface tensions to those in the literature showed

some substantial differences. The surface tension displayed a large decrease for #1

plastics (32.7 dynes/cm) which was 10 dynes/cm less than the literature value. Plastic #3

39

(32.4 dynes/cm) decreased about seven dynes/cm from the literature value. The
remaining plastic types were close (within 1 or 2 dynes/cm) to their respective untreated
surface tension literature value. The surface tension values for each plastic category are
displayed in APPENDD( B. Within each reading ﬁngerprints are sorted based on their
processing result, with a success rate shown below the number of ﬁngerprints. Surface
tension values within each plastic id number that created the largest success rate were #1:
36 dynes/cm (100%), #2: 30 dynes/cm (66.7%) and 38 dynes/cm (66.7%), #3: 32
dynes/cm (75%), #4: 36 dynes/cm (100%), #5: 34 dynes/cm (100%), #6: 34 and 36
dynes/cm (100%), and #7 (other): 34 dynes/cm (100%). However, it is important to note
the small sample sizes for several of these classiﬁcations. For nearly all plastic types,
except #3, a higher surface energy resulted in a higher success rate. Those items with a
reading of 32 dynes/cm (#1, #2, #3, #5, #6 and #7) usually resulted in the lowest success
rate (six of the seven plastic types).

Table 10 Surface Tension Readings

 

 

 

 

 

 

 

 

 

 

Plastic S.T. Literature <30 30 32 34 36 38 Total Average
ID # Values for U.T.P. F.P. S.T.
(dynes/cm)
1 43 O 2 24 13 2 0 41 32.7
2 33 0 28 87 40 12 3 170 32.5
3 39 — 40 O 0 4 1 O 0 5 32.4
4 3 1 0 2 0 7 l 0 10 33.4
5 29 6 l7 l3 7 0 0 43 31.1
6 33 4 6 7 2 1 0 20 3 1 .2
7 0 0 2 3 0 0 5 33.2
Totals 10 55 137 73 16 3 294

 

 

 

 

 

 

 

 

 

 

Surface tension reading occurrences with their respective plastic identiﬁcation category.
Each reading (dynes/cm) corresponded to a ﬁngerprint within that plastic identiﬁcation
category. An overall average surface tension reading was calculated for each plastic
identiﬁcation category. Literature values for untreated surface tensions for their
respective plastic type are displayed in dynes/cm. #=Number U.T.P. = Untreated plastics
F.P.=Fingerprints S.T.=Surface Tension

40

 

Proﬁlometry

A proﬁlometer was used to analyze the surface texture of a subset of plastic items

and note correlations between the readings and processing results. Due to the

proﬁlometer’s thickness limitations as well as the ﬂatness requirement, only eight

samples were analyzed (Table 11). Readings were taken adjacent to two ﬁngerprints, one

that was enhanced and the other which was not. Average surface texture readings ranged

from 32779.3 amps to 2043353 amps, with the roughest reading being a #2, white, rough

textured Rid-X container (sample 76~b), while the smoothest was #2 white, glossy

Michigan Cottage Cheese Lid (sample 43-a). In half of the cases the region with the

higher surface tension exhibited a higher ﬁngerprint enhancement success rate (EP +

EP/LD), while in the remainder the opposite was the case.

Table 11 Proﬁlometer Analysis

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Plastic Item Rinsing Proﬁlometer Reading (Amps) Average
Result Proﬁlometer
Reading (Amps)
Red Lid #65 65-a-BP 45846 58573 83485 62634.6
65-b-EP 59373 71517 49472 60120.6
Blue Lid #66 66-a-BP 56618 59992 72655 63088.3
66-b-EP 42665 503 19 27945 40309.7
Dinty Moore Lid 47-a—LP/D 78328 80187 81 125 79880.0
#47 47-b-EP 46878 35746 53341 45321.7
Michigan Cottage 43-a—EP/LD 37699 30899 29740 32779.3
Cheese Lid #43 45-b-EP 31801 45076 29399 35425.3
Brummel & Brown 48-a-LP/D 86874 134802 90494 1040567
Lid #48 48-b-EP/LD 105904 13 1 162 150979 1293483
Rid X Cont. #76 76-a-BP 83420 113000 91804 96074.7
76-b-EP 226006 165000 222000 2043353
Chlorox2 Cont. #78 78-a-EP 30100 56600 48900 45200.0
78-b—BP 83000 92700 100000 91900.0
Bacteriostat Cont. 75-a-BP 74000 28900 47000 49966.7
#75 75-b-EP 151000 163000 145000 1530000

 

The plastic items with the individually labeled ﬁngerprints’ sample number and their
corresponding rinsing result. Near each ﬁngerprint, three separate readings were taken
and an overall surface roughness average was calculated. EP-Enhanced Print, EP/LD-
Enhanced Print/Lost Detail, LP/D-Lost Print/Detail, and BP—Black Powder Engulfed.

41

 

Cyanoacrylate Chamber Variation

Eight items, 88-a - 94-f, encompassing 38 ﬁngerprints, were cyanoacrylate fumed
in a Mason Vactron, MVC 5000 and processed using the powdering/rinsing sequence
identiﬁed in the Materials and Methods section. The processing results for each category
were: 10-“EP” (26.3%), 12-“EP/LD” (31.6%), ll-“LP/D” (28.9%), 0-“LP/B”, 0-
“LP/BF”, 5-“BP”, 0-“PR/NBP”. These results were similar to those of the main sample
set which were fumed in a Fisher Hamilton cyanoacrylate chamber, in that they had
nearly the same number of enhanced prints as the main sample set (57.9% vs. 53.1%,
respectively). While the main sample set had more successfully enhanced prints than any
other result, this sample set had slightly more enhanced prints/lost detail results. The third
most frequent result was lost print/detail for‘both sample sets.
Inter-Individual Variability Analysis

Sixteen #2 Kroger grocery bags and ﬁve #2 zip close plastic bags were laid on a
table and handled by anonymous individuals to determine whether the rinsing process
was affected by inter-individual variation. These yielded the following results: 16 Kroger
grocery bags (1 1-“EP” (68.8%), 1-“EP/LD” (6.25%), 4-“LP/B” (25.0%)) had an overall
successful result of 75% which was consistent with the main sample set. The lost
print/blurred result occurred more frequently (25.0%) than the main sample set (8.6%).
The results obtained for the 5 zip close plastic bags were 1-“LP/D” (20.0%) and 4-
“LP/B” (80%). Overall, the zip close bags did not produce any enhanced prints or

enhanced prints/lost detail results.

42

Rinse Solution Variation Analysis

Table 12 displays the results obtained from using eight different rinsing solutions
over eight sets of two latent prints that were placed on separate #2 high-density
polyethylene Kroger grocery bags. A number of different reactions occurred as a result of
the variations in solution compositions. The only solution to produce enhanced print/lost
detail results was eight. Although it did have a successful result, it did not produce the
same quality result that the original solution did. A majority of these solutions did not
effectively enhance the print and four of the eight exhibited difﬁculties in removing the

background black powder while three produced “PR/NBP” results.

43

Table 12 Rinsing Solution Results

 

 

 

 

 

 

 

 

 

 

 

 

Solution Rinsing Result Processing
Result
1 -N After the 5th rinse, prints remained light, and most of the black LP/BP
Hep powder wiped off after each rinse. Surrounding black powder
began to build making the plastic background very dark.
2 -M After the 6th rinse, prints started to darken, but remained much LP/BP
Hex lighter in comparison to the surrounding area where the black
powder became thick and dark. The powder was thicker than in
solution one.
3 -EA After the 4‘11 rinse the entire bag remained black and black BP
Hex powder would not wipe off. It appeared to stick to the plastic
and the powder felt thicker and rough with each successive
rinse. Thick precipitate formed in the bottom of the solution
ﬂask.
4 Hep After the 4th rinse and all following rinses, no black powder PR/NBP
adhered to prints or background. Prints did not darken.
5 -EA After the 4m rinse entire plastic remained black and black BP
Hep powder would not wipe off. It appeared to stick to the plastic
and the black powder felt thicker and rough. Thick precipitate
formed in the bottom of the solution ﬂask.
6 -N After every rinse, the plastic wiped clean, and the black powder PR/NBP
-EA would not adhere to prints. The print could be seen obliquely.
Hex
7 -Hex After the SFrinse and all following rinses, the print remained PR/NBP
-Hep light and no black powder adhered. The background black
, powder wiped clean and free of interference after each rinse.
8 -M After the 1St rinse, prints cleared up a little and were light. EP/LD
+E Multiple rinses darkened print, but after six rinses, the print
+AA remained light. One print blurred and one was moderately
Hep enhanced allowing for few details to be seen. Excess black
powder that was removed by sponge did not appear to drain off
with of smrge with rinsing solution like other six solutions.

 

The rinsing solution was varied in composition and ratio and noted below each solution
number. The observed results from each are displayed. -N=no Ninhydrin present,

- =no methanol present, -EA=no ethyl acetate present, +E=ethanol present, +AA=acetic
acid present, Hep=heptane, Hex=hexane

Microscopic Analysis of Enhancement Progression

Scanning Electron Microscopy

Two separate sets of images were taken to help determine microscopically what

occurred between the plastic item, cyanoacrylate, black powder, and the latent ﬁngerprint

 

through the powder/rinse cycles. The ﬁrst set of images (Figure 23) depicts four separate
latent prints that were processed to different stages of the cycle (Table 3). The ﬁrst image
(Figure 23 a) displays an identiﬁable print whereas the powdered ﬁngerprint (Figure 23
b) shows that the powder not only adhered to the ridges but-it also collected in the
furrows. After the ﬁrst (Figure 23 c) and ultimately the third rinsing cycle (Figure 23 d),
the ridges became more distinct and sharp as the excess black powder was removed,

allowing for better visibility of minutiae.

  
     

ure 23 SEM Ima le Prints

. - '- . 7" ‘.
. .

             

‘ . . 1..
tags}; ' '
1.9.923: 3:19.121: "fr ,
, . V .qﬁbﬁ‘gﬁﬁyﬁ'; ‘ ‘ ‘93. .
c we". ems r s r

  

  

   

   

m. ~ ' .1 ‘ - ..
SEM images of a cyanoa rylate fumed only print (a), a cyanoacrylate fumed and
powdered print (b), a cyanoacrylate fumed, powdered and rinsed print (c), and a print that
had been cyanoacrylate fumed then powdered/rinsed three times (d). Note the ridges in
the black powdered print appear to be closer together and not as distinct as the third
rinsed print where they are more distinct.

The second set of images (Figure 24) is of one latent print that was processed and

imaged following each step (Table 3) after having applied a layer of gold. An attempt

45

was made to image the ﬁngerprint without applying successive layers of gold, but the
signal was too weak, producing a dark screen with a very small amount of ﬁngerprint
visible. The cyanoacrylate fumed ﬁngerprint (Figure 24 3) produced an image that was
much like that in Figure 23 (a). The ﬁngerprint however, became degraded and lost detail
after the powdering step (Figure 24 b) and ultimately after the ﬁrst (Figure 24 c) and third
rinsing step (Figure 24 d). The black powder would not wipe from the ﬁngerprint, thus

the minutiae were lost and the print was less identiﬁable.

re 24 SEM Ima_es of a Sin Ie Print

 

SEM images of a single fingerprint sample: a cyanoacrylate fumed only print (a), the
ﬁngerprint having been cyanoacrylate fumed and powdered (b), the ﬁngerprint having
been cyanoacrylate fumed, powdered and rinsed once (c), and the ﬁngerprint that had
been cyanoacrylate fumed then powdered/rinsed three times (d). A layer of gold was
applied after each step. Note the cyanoacrylate fumed print was completely identiﬁable,
but the ﬁngerprint minutiae started to disappear and blur with successive powder/rinsing
cycles as seen in the third rinse.

46

Elemental Analysis of Enhancement Progression
Scanning Electron Microscopy — Energy Dispersive X-Ray Spectrometry

SEM-EDS was employed to analyze chemically what occurred during the
powder/rinse cycles among the plastic, ﬁngerprint, cyanoaCrylate, powder and hexane. A
cyanoacrylate fumed print was analyzed, comparing a ridge location with a furrow
location. An overlaid graph of the SEM-EDS output is shown in Figure 25. Note the
tremendous similarity in the two graphs. Similarly, an overlay resulting from two
different ridge locations is shown in Figure 26. The Center for Advanced Microscopy at
Michigan State University uses carbon as the coating material for SEM—EDS.
Unfortunately, carbon, being the main element in black powder, as well as in ﬁngerprint
components and the wash solution, meant that reasonable quantitative analysis could not
be made (note the large carbon peak in all graphs). Any elements lighter than carbon
were also undetectable, while a few other substantial peaks, including titanium
(presumably a whitener in the bag) and calcium, were seen. An attempt was made to
analyze the same samples without carbon coating however, the signal was not strong
enough to send elemental and topographical information back to the detector, producing

an uninformative image.

47

Figure 25 SEM-EDS Cyanoacrylate F umed Print - Ridge and Furrow
Thermo l‘iORAN

 

 

anCOO

 

 

KeV

An SEM-EDS overlay of a sample that has been cyanoacrylate fumed is displayed. One
line designates the result for the furrow only of that print and one line designates the

result for the ridge only (*)

48

Figure 26 SEM-EDS Cyanoacrylate F umed Print-Ridge 1 and Ridge 2
Thermo NOR/3N

.'
I
I
I

 

mﬂDCOO

L...

 

“m

 

An SEM-EDS overlay of a sample that has been cyanoacrylate fumed is displayed. One
line designates the result of one location on the ridge of that print and the other line
represents another location on the same ridge. The locations produced very similar results
making it difﬁcult to make a distinction between the two. The only difference that can be
seen is at the magnesium peak.

Discussion

The primary purpose of this research was to assess the utility of a ninhydrin
hexane solution for processing latent prints on plastic materials following cyanoacrylate
fuming and powdering. Over 100 plastic items and nearly 300 latent prints were
processed to identify the most effective rinsing solution for enhancing ﬁngerprints which
had become engulfed in black powder and were no longer identiﬁable. The research was
also aimed at identifying the characteristics of plastics that made them conducive to
achieving successful results, where the ﬁngerprint was enhanced such that ridge detail
and minutiae could be easily discerned, or those that were enhanced but lost detail

through the loss of minutiae. Plastic characteristics such as plastic type. presence or

49

absence/removal of inked printing and/or labels, color, surface ﬁnish, surface tension,
and surface roughness were analyzed to evaluate their inﬂuence on the rinsing method
success. Microscopic examinations were made to determine what changes occurred to the
print between the cycles of powdering and rinsing, as was elemental analysis to examine
the chenrical variations among the plastic, cyanoacrylate, powder and rinsing solution
during the powder/rinse cycles.
Item Collection and Sample Sizes

Plastic household items were collected from donations. The most common plastic
types received were #2 (55 items) and #5 (17 items) while plastic types #3 and #7 were
fewest, represented by only two items each, with the other types in between (APPENDIX
A). At ﬁrst glance the disparity in plastic types might seem to nullify the utility of the
research presented here however, this is likely not the case. While some plastic types
were underrepresented, overall the sampling represents those types that occur in a day to
day setting. The items were collected by individuals who were requested to bring in any
plastic items they used, so it likely is a reasonable representation of each plastic type’s
occurrence.
Processing Results

As a result of this research, seven different processing outcomes were noted (see
Results and Figures therein for details on these). Once a latent print was enhanced (print
was enhanced or enhanced but lost detail) which occurred in 53.1% of the instances,
further processing either left it unharmed and identiﬁable (usually on the more textured
surfaces), or it began to wipe away (on smoother or glossy surfaces). Prints and

background that started to darken from the black powder typically darkened further with

50

additional rinses. There was no print recovery with more washes for those items that
began to lose detail through loss of minutiae or blurring as they continued to lose detail
and blurred. “PR/NBP” prints remained after multiple rinses however, further processing
did not enhance the print. Latent prints that were identiﬁable as a result of the initial
powder application often were further enhanced through rinsing, but at times the print
disappeared.
Plastic Types

To uncover what properties inﬂuenced the success of enhancement, different
plastic types were evaluated (Table 1). Those types with the greatest percent of enhanced
prints were #3 and #7 both at 60% (Table 6). It is important to note the small sample size
for these however (5 prints each), so the results may not accurately represent their
functional processing outcome. For plastic types with more than 40 ﬁngerprints (#1, #2,
and #5), #2 plastic types had prints that were enhanced nearly 51% of the time, while the
others were < 50%, as were types #4 and #6 with smaller sample sizes. Plastic types #1,
#5 and #7 lost details >30% of the time. Plastic #6 items tended to become further
engulfed in the black powder (35.0%). From these results, a general conclusion is that the
plastic type most likely to beneﬁt from the powdering/rinsing technique is #2, while #3
and #7 also seem to be effective. However, for all plastic types some portion of the items
became enhanced using the technique; in no case is the method to be fully avoided based
on plastic type, assuming it is the last method available for latent print enhancement.
The Inﬂuence of Color

The plastic items were further differentiated based on color (Table 7). To produce

variations in plastics, colorants are added that could potentially inﬂuence the prints

51

ability to adhere or be enhanced. Orange and red items had the highest enhancement rates
(100% and 71.4%, respectively) however, their sample sizes were small (3 and 7 prints,
respectively). Plastic colors represented by large sample sizes (10 or more ﬁngerprints)
had lower success rates, with gray items being the most successful at 70%. Clear, green,
and white containers (excluding bags) were the least successful based on the combination
of the percent of enhanced prints (52.7%, 50.0%, and 49.6%, respectively) and the
percent of lost prints (31.2%, 25.0% and 32.5%, respectively). On the other hand, clear
and white bags were successful 75.9% of the time. It is possible that the color additives
that are put into plastics may bond or repel ﬁngerprints, cyanoacrylate, or powder, and
inﬂuence the print’s ability to adhere to the surface. Most likely however, this is not the
case. The colors with large sample sizes had quite average rates of enhancement (around
50%), indicating color additives do not affect the enhancing results.
The Inﬂuence of Surface Finish and Surface Roughness

Surface ﬁnishes were noted for items as either “glossy”, those items that were
shiny and smooth to the touch, “smooth”, those items that had a ﬂat surface, “textured”,
those items that were mildly rough, and “rough textured”, those items that had pits on the
surface. When the surface roughness increased, the success rate for developing enhanced
prints also increased. Rough textured items produced the highest level of enhanced prints
(67.5%), followed by textured and smooth, while glossy items were the least successful
(40%). One possible reason latent prints left on rough textured items were more often
enhanced is that the prints were better able to adhere to the item by ﬁlling the valleys
(pits) of the plastic. In contrast, the smoother surfaces allowed the print to be easily

wiped off. This rinsing technique proved most useful for rough textured #2 items, as they

52

produced a large number of enhanced results (69.4%). Plastic #5 white, glossy items
rarely beneﬁted from this technique (36.0%), probably because the ﬁngerprints are more
exposed to the rinsing solution and/or the prints are not able to adhere as strongly.

Interestingly, when surface texture was tested using proﬁlometry, the
enhancement showed no correlation with the surface texture. However, it is important to
note that only eight items were evaluated using this method, because of the technical
requirements of the instrument. Each of the eight items had one successful and one failed
print that had been processed using this rinsing technique. Proﬁlometry was used to
distinguish the surface texture at the microsc0pic level, and in half the cases the enhanced
print was on the rougher surface, while half the time it was on the microscopically
smoother surface. Therefore, at that level surface texture does not seem to be important
for success.

For ﬁve of the eight items (#43, #47, #48, #75 and #78), the surfaces for
successful/failed prints appeared visually to be the same, while on the remaining three
(#65, #66 and #76) there was a clear distinction in roughness. In two of the three
remaining items, #65 and #66, the successful print was on the visibly rougher surface
however, at the microscopic level the failed print was on the rougher surface, or the
proﬁlometer produced results opposite from visual inspection. On the other hand, for
item #76 the successful print was on the visibly smoother surface which was supported
by proﬁlometer readings. It appears that the proﬁlometer is measuring the surface at such
a detailed level, it does not fully evaluate the overall roughness or smoothness of the

item. While proﬁlometers are not readily available to lab personnel, the visual evaluation

53

appears to be sufﬁcient when determining the surface ﬁnish which is helpful in

determining whether the rinsing technique should be employed.

The Inﬂuence of Inked Printing and Adhesives

Locations of inked printing and areas where labels had been removed were
evaluated to identify if there was a correlation between these plastic characteristics and
processing results. While surface treatments are applied to increase the retention of the
inked printing and labels, additives also may affect the success of obtaining an enhanced
print. Inked printing appeared to have a negative effect on the processing, being enhanced
36% of the time, while 48% of latent prints were lost. It seems likely that when the inked
printing is applied to the surface, the printing smoothes it, resulting in a glossy texture
that does not retain the print however, it may not smooth #2 plastic surfaces to such an
extent allowing for more successful results. Typically #2 plastic items with inked printing
achieved enhanced prints 50.0% of the time which may be due to a variation in the
surface treatments and additives used for these plastics.

In contrast, regardless of whether a label had or had not been present on the item
prior to leaving the latent print, the prints were enhanced 55% of the time. However, in
some cases a print left where a label had been removed lost detail (e.g., Figure 10) while
in other cases it generated successful results (e. g., Figure). Latent prints that were placed
half on and half off of a location where a label had been removed exhibited the same
success rate for both sides of the print (33.3%). Naturally, a label or the treatment beneath
it need not be single entities. Manufacturers use many different labels and adhesives
containing different chemicals based on the requirements for the container, including if it

will contain liquid or is likely to become wet (e.g. laundry, bath, and food containers), if

54

solvents come into contact with it (e.g., a rubbing alcohol bottle), or if it will be heated of
frozen, etc. It is not surprising that the labels and adhesives behaved differently during
the rinse procedure due to these variations.

The Inﬂuence of Surface Tension

Surface tension was evaluated using ACCU DYNE TEST Markers to determine
how surface energy inﬂuenced the retention and enhancement of latent prints (Table 10).
Since surface treatments are generally applied to increase surface energy, the resulting
value for the plastic items might be predicted to be greater than that of the literature value
(Hemandez et al. 2000). In contrast, a number of surface tension values were found to be
lower than published standards. For instance, the average surface tension for #1 plastic
items (32.7 dynes/cm) was 10 dynes/cm lower than the literature values, while plastic #3
(32.4 dynes/cm) was about seven dynes/cm lower. These decreases may suggest that no
surface treatment had been applied, or certainly no treatment designed to increase surface
tension, and in fact the opposite could be true. In this regard, one notable feature is that
all plastic types had average surface tension values around 32 dynes/cm. It is possible
that this surface tension is ideal for adhering inks and labels, or to otherwise generate
characteristics sought by the manufacturers for commercial products.

Six of the seven plastic types exhibited a trend showing that as surface energy
increased the percent of enhanced prints also increased, the sole exception being type #3,
which displayed the opposite trend (APPENDD( B). Plastic types #1, #2, #3, #5, #6, and
#7 each had average surface tension readings near 32 dynes/cm. In general, enhancement
success rates were lower with a surface tension reading of 32 dynes/cm whereas readings

that were greater than 32 dynes/cm had a higher success rate (except #3 items). The

55

correspondence of surface tension with print enhancement suggests that this surface
energy helps to increase the bonding strength of the latent print to the surface, which
allows for further powder/rinse cycles and enhancement of the print with few or no
details lost.
Processing Variations

The use of two different cyanoacrylate chambers, which generated very similar
enhancement results, demonstrated that the processing technique was not inﬂuenced by
chamber variations. It appears that any differences in the amount of cyanoacrylate
vaporized, cyanoacrylate adhering, and the amount of humidity in the chamber did not
affect the overall enhancement results. Inter-individual variability demonstrated that
processing results were independent of latent print sources as well.
Rinsing Solution Component Analysis

Modiﬁcations were made to the original rinsing solution (Scarborough 2001) and
used to process #2 grocery bags that had successfully been enhanced with the original
solution. An alternate solution described by Wertheim was also evaluated. From these
experiments, it became apparent that methanol was required to fully dissolve the
ninhydrin, in that when methanol was not present the print would not return to the dark
print that was achieved by the original solution. Ninhydrin and hexane helped to darken
the latent print as the ninhydrin may have been adhering to the ridges and minutiae and
the hexane facilitated this process, resulting in a darkened outline although there was no
indication of purple coloration. It may also be possible that the ninhydrin and hexane may
be assisting the black powder in adhering to the ridges in both identiﬁable and engulfed

prints. When ethyl acetate was left out of the solution, a thick precipitate formed that

56

prevented the solution from thoroughly mixing. As a result, the ﬁngerprints were not
enhanced. Also, in the absence of ethyl acetate, the rinsing solution did not remove the
excess background black powder from the item, increasing the background darkness until
the print became engulfed. Replacing hexane with heptane resulted in the black powder
being wiped from the print, and further powder/rinsing did not darken the print to make it
identiﬁable. Finally, the eighth rinsing solution (W ertheim), consisting of ninhydrin,
ethanol, ethyl acetate, acetic acid, and heptane, provided the best enhancement when
compared to the other seven modiﬁcations. It did not however, produce the impressive
results that the original solution achieved. Since both the seventh and eighth solutions had
heptane as a reagent, the latent print was not darkened as extensively as when hexane was
present, indicating that the solution requires hexane in order to produce the most
successful results.
Scanning Electron Microscopy Analysis

The SEM was used to image four separate latent prints (Figure 23), including a
cyanoacrylate fumed only print, a cyanoacrylate fumed and powdered print, a
cyanoacrylate fumed, powdered and rinsed once print, and a cyanoacrylate fumed,
powdered and rinsed three times print. It is important to note that the ridges are light in
comparison to the furrows. This shows that the ridges are closer to the detector and this
contrast increases as the furrows increase in distance from the detector when the powder
is removed. The cyanoacrylate fumed image (Figure 23 a) was identiﬁable, but did not
have sharp details. The print that was powdered (Figure 23 b) started to blur as the
powder settled in the furrows causing the ridges to blend together, but after the ﬁrst rinse

(Figure 23 c) the black powder was removed from the furrows and the ridges became

57

more distinct and clear. Ridge detail was further improved after the third rinsing (Figure
23 d). The contrast differences shown in the Figure 23 images demonstrated the
difference in depth between the low points (furrows) and high points (ridges) of the print.
These contrast differences increase from Figure 23 (a) thrOugh Figure 23 (d) as the print
undergoes more rinsing cycles and the black powder that had settled in the furrows may
be removed as a result.

In the second set of images (Figure 24) a single ﬁngerprint was placed on a white,
#2 grocery bag and processed to various stages of the powdering/rinsing cycle as was
done for the previous SEM images and were imaged after each step. One major
observation was made. After successive applications of gold, the latent print could no
longer be rinsed to produce an enhanced print. Upon evaluation of the black powdered
image (Figure 24 b), it appeared that the powder may be adhering to all areas where the
gold coating was applied, outlining the structures of the print, ultimately producing a
partially identiﬁable image. The ﬁrst and third rinses (Figures 24 c and d) produced
blurred images that had fewer areas that could be used for identiﬁcation. As the layers of
gold were applied, no distinction could be made between the ridges, resulting in a print
that showed little detail and was of little value.
Scanning Electron Microscopy — Energy Dispersive X -Ray Spectrometry Analysis

An SEM-EDS was employed to image and elementally determine the changes
that occurred between stages of the powdering/rinsing cycle among the print,
cyanoacrylate, powder, and rinse solution. The high resolution of this procedure meant
that a ridge and furrow could be individually tested. Because cyanoacrylate is an organic

compound, changes in carbon levels after each step were to be examined. Unfortunately,

58

the only coating element available for these experiments used carbon, resulting in off
scale carbon readings for all portions of the plastic item. However the large number of
organic compounds involved in the procedure, including the plastic itself, some
ﬁngerprint components, the cyanoacrylate, powder, ninhydrin, and rinse solution, means
that a variable other than carbon will need to be investigated if this technique is to prove
useful. Overlaying ridge and furrow graphs (Figures 25 and 26) showed no notable
differences in the levels of elements except for calcium and titanium. Although calcium is
potentially a component of the ﬁngerprint, it is not found in any of the other reagents.
Titanium would not be contained in any component except the bag itself, and it is widely
used as a whitener for plastics and other products. Differences between the ridges and
furrows could be due to the amount of whitener in the #2 plastic bag on which the print
was placed. Different locations on the bag may demonstrate a range in the amount of
these elements, or result from small ﬂuctuations in the SEM-EDS procedure itself.
Regardless, because of carbon coating the technique was not helpful in understanding
elemental changes occurring during the rinse procedure. Although alternative coating
methods are not currently available at MSU, it is possible to coat samples with materials
such as nickel or a silicon lubricant, and thus it may be possible to collect qualitative and
quantitative data regarding the amount of cyanoacrylate, black powder, and rinsing
solution (hexane and ninhydrin) during the rinsing process.

Elemental analysis may also help to determine if the black powder is solely what
is causing the ﬁngerprint to turn black, or if the ninhydrin and hexane assist in darkening
the ridges and minutiae in the ﬁngerprint. The SEM-EDS may also provide information

on what causes the latent print to stay light in those trials where the print remained but

59

the black powder was not adhering to it or the background. The SEM—EDS could also
help in determining where the black powder was adhering. Other elemental analysis
techniques such as atomic absorption, inductively coupled plasma-mass spectrometry,
and inductively coupled plasma — optical emission spectroscopy could be employed for
determining chemically what occurs among the components involved in the

powder/rinsing cycles.

Potential Mechanisms of the Rinsing Method

Plastic types, additives, surface treatments, surface textures, and surface tensions
are designed to manipulate the physical characteristics of a plastic, and therefore might
react differently with a number of chemicals analyzed in this research, including those in
the ﬁngerprint itself. The ﬁrst step in the rinsing technique was cyanoacrylate fuming,
which coats the print, helping to stabilize it. Cyanoacrylate, widely used for latent
ﬁngerprint development, undergoes anionic polymerization with a weak base and
becomes stabilized with a weak acid (Courtney and Verosky 1999), thus pH extremes
may act to decrease the success of the rinsing technique. While the pH of these plastics
was not tested, and it is not clear if they differ, this is one variable that could inﬂuence
the success of the technique. These changes could alter the amount and location of
cyanoacrylate polymerization and ultimately alter the environmental factors affecting the
rinsing technique.

Surface texture also inﬂuences the success of the technique. Here again the
cyanoacrylate may be affected, in that the rougher surfaces may act as a better adhesive

for the polymer. On the other hand, glossy and smooth items do not have these valleys or

60

pits on the surface for the cyanoacrylate to adhere to, making the print easier to wash
away.

The function of the wash solvents and ninhydrin are also interesting to consider.
SEM examination of a single ﬁngerprint after each step in'the processing cycle showed
that the gold coating blocked subsequent enhancement of the print. This indicates that the
cyanoacrylate may be permeable (or being made permeable by the various solvents
applied), allowing rinsing solution and black powder to reach the latent print beneath the
cyanoacrylate. However, it is also possible that the rinsing solution and powder are
reacting with the cyanoacrylate and not the print itself, a process that would also be
stopped by the gold coating.

When examining the black powder’s role in ﬁngerprint enhancement, two
possibilities exist. One is that the powder not only adheres to the latent print, but also
adheres to the cyanoacrylate. If the cyanoacrylate binds predominantly to the print, then
the powder also would adhere to the print, enhancing it. On the other hand, if the
cyanoacrylate binds over a larger region, the powder may engulf the print, and perhaps
adhere to other areas of the plastic as well.

The hexane-based ninhydrin solution may be serving three purposes. First, it
could help dissolve cyanoacrylate, exposing the latent print. Second, the solution may
help enhance, darken, and sharpen ridge detail of the print. Third, the solution wipes
away excess black powder, exposing just the ridges and minutiae for identiﬁcation. When
comparing heptane versus hexane, rinses that contained hexane proved superior to those
that contained heptane. It is possible that the heptane reduced the solubility of the

ninhydrin, or otherwise negatively impacted one of the other reagents. It may also have

61

reacted with cyanoacrylate differently, perhaps making it less soluble (see above). Other
variations from the original rinsing solution described by Scarborough (2001) were
evaluated and it appears that the original formula was most successful. However, it may
prove useful to further examine different compositions to determine if there are more
effective solutions or if speciﬁc solutions are effective for speciﬁc plastic items and
conditions. The reagents could possibly be replaced in the original rinsing solution with

alcohols, ketones, ethers and alkanes.

Overall Recommendations and Observations

The sequence for mixing the rinse solution should be followed as outlined in the
materials and methods section, otherwise the ninhydrin will not completely dissolve,
resulting in sub optimal processing results. When applying the rinsing solution to the
plastic items, a glass or plaster bowl should be used, which allows the black powder
removed from the plastic item to settle to the bottom, and provides a clean rinse solution
at the top for further applications. Firm pressure should be applied to the plastic item
when drawing the foam brush across the sample to remove the excess black powder.
Using the foam brush to trace the pattern of the print can produce a darker image, as the
excess black powder from the brush may stick to the ridges and darken them, resulting in
more distinct ridge details. However, at times, the ridges can be wiped away. Therefore,
it is important to photograph the latent print after each step in the powder/rinse cycle. In
some instances, a print that is initially identiﬁable may wipe clear or lose detail after only
one rinse, whereas at other times, one rinse results in excellent detail (e. g. Figure 13).
Nitrile gloves should be worn when handling the rinsing solution as it can penetrate latex

gloves.

62

After being processed with black powder, some plastic items develop latent prints
that are engulfed in the powder and are no longer visible or identiﬁable. Unless the black
powder can be removed, the print is of no value. Though the rinsing procedure did not
prove useful in removing excess powder in all cases, it did provide a new step for
recovery of minutiae that were not identiﬁable through black powder. The technique
works best on rough textured items and success is independent of presence or location of
a removed label. It is less successful on smooth or glossy items, as the print is more likely
to wipe from the surface. However, this technique ultimately can be used as a last resort
for any surface type as enhancement can ultimately work on any plastic. Further
processing should not be attempted when the amount of black powder adhering starts to
increase and the print begins to lose detail or becomes blurred, as the latent print will
continue to darken, lose detail, and blur. This rinsing technique also provides the
possibility of developing prints that were not visible after application of black powder
alone. Although there are exceptions to all of these cases, it is suggested that if the latent
print is of little or no value and photographs have been taken, using this technique can
provide an additional processing step, increasing the probability of producing an

identiﬁable print.

63

APPENDICES

APPENDIX A

Sample Characterizations and Processing Results

Plastic items are detailed with labeled ﬁngerprints for each item. If the ﬁngerprint was
placed over an inked printing, "Inked Printing" is noted. If a ﬁngerprint was placed where
a label was removed, "Label" is noted. If there was no label initially present where the
ﬁngerprint was placed, “No Label” is noted. The absence of notations in the inked
printing/label area, indicates that no label was removed or no label had been present
where the ﬁngerprint was placed. In addition, details regarding the plastic’s
characteristics are noted including the plastic ID number, color and surface ﬁnish. The
surface tension (dynes/cm) for each ﬁngerprint is noted as well as the overall processing
result.

EP-Enhanced Print

EP/LD-Enhanced Print/Lost Detail

LP/D-Lost Print/Detail

LP/B-Lost Print/Blurred

LP/BP—Lost Print/Background Black Powdered
BP—Black Powder Engulfed

PR/NBP-Print Remains/No Black Powder Adhering

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APPENDIX B

Surface Tension and Plastic Type Processing Results

The surface tension values within a plastic category are displayed. Within each surface
tension reading, the ﬁngerprints are sorted based on their processing result, with a
success rate (EP + EP/LD) calculated below the number of ﬁngerprints.

Plastic ID. #= Plastic Identiﬁcation Number F.P.=Fingerprints

EP-Enhanced Print

EP/LD-Enhanced Print/Lost Detail

LP/D-Lost Print/Detail

LP/B-Lost Print/Blurred

LP/BP-Lost Print/Background Black Powdered
BP-Black Powder Engulfed

PR/NBP-Print Remains/No Black Powder Adhering

78

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Plastic <30 30 32 34 36 38 Total Avg.
ID # F.P. S.T.
1 0 2 24 13 2 0 41 32.7
0.0% 41.7% 46.2% 100%
Z-LP/B EP—Z EP-2 EP/LD-2
EP/LD-8 EP/LD-4 '
LP/D-9 LP/D-l
LP/B-l LP/B-3
LP/BP-2 LP/BP-l
BP-2 BP-2
2 0 27 85 40 13 3 168 32.6
66.7% 55.3% 55.0% 61.5% 66.7%
EP-8 EP-32 EP- 1 3 EP-8 EP-l
EP/LD- EP/LD- EP/LD-9 EP/LD-O EP/LD-
10 15 1
LP/D-6 LP/D-l l LP/D-7 LP/D-l BP- 1
LP/B-O LP/B- l 3 LP/B—6 LP/B-O
LP/BP-O LP/B P- l LP/B P-O LP/B P-O
BP-3 BP-l l BP—S BP-4
PR/NBP-
2
3 0 0 4 1 0 0 5 32.4
75.0% 0.0%
EP/LD-3 PR/NBP-l
PR/NBP-
l
4 0 2 0 7 1 0 10 33.4
50.0% 28.6% 100.0%
EP-O EP-l EP-l
EP/LD-l EP/LD-l
LP/D-O LP/D-l
LP/B-O LP/B-O
LP/BP-O LP/BP-O
BP-l BP-3
PR/NBP-l
5 6 17 13 7 0 0 43 31.1
33.3% 52.9% 23.1% 100.0%
EP-Z EP-S EP-2 EP-3
EP/LD EP/LD-4 EP/LD-l EP/LD-4
-0 .
LP/D-4 LP/D-3 LP/D-4 LP/D-O
LP/B-O LP/B-O LP/B-O LP/B-O
LP/BP- LP/BP-O LP/BP-2 LP/BP-O
0
BP-O BP-3 BP-2 BP-O
PR/NBP- PR/NBP- PR/NBP-O
2 2

 

79

 

 

 

 

 

 

 

 

 

 

 

 

Plastic <30 30 32 34 36 38 Total Avg.
ID # F.P. S.T.
6 4 6 7 2 l 20 3 1.2
0.0% 50.0% 42.9% 100.0% 100.0%
BP-4 EP-O EP- 1 EP/LD-Z EP/LD- l
EP/LD-3
LP/D-2 EP/LD-Z
LP/B-O LP/D- l
LP/B P-O BP-2
BP-l PR/NBP-
l
7 O O 2 3 0 5 33.2
0.0% 100.0%
LP/D-2 EP-2
EP/LD-l

 

 

 

 

 

 

 

 

 

 

 

 

80

 

REFERENCES

81

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Richards EP. “Phenotype v. Genotype: Why Identical Twins have Different
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Saferstein R. Forensic Science Handbook. Vol. II. Prentice Hall. Upper Saddle River,
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Scarborough S. “Success of hexane—based ninhydrin amino acid reagent processing on
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Seradyn, “Polystyrene and Carboxylate-Modiﬁed Microparticles”. 1999.
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Stanford N anofabrication Facility
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SWGFAST. http://www.swgfastorg/Glossary Consolidated ver 1.pdf

The Societies of Plastics Industry. http://www.socplas.ch/

The University of Southern Mississippi and School of Polymers and High Performance
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http://www.pslc.ws/macrog/work/recwle.htm

Van Iseghem LC. “Coating Plastics - Some Important Concepts from a Formulators
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Wertheim PA. “Ninhydrin: Basic to Advanced”. Forensic Identiﬁcation Training
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