THE EVALUAfiON OF THE BAUSCH AND 10MB EWCTANCE ' WHOTOMETER FOR THE COMPARISON OF MlNLJTE PAW? 59£~C§MENS ' Thesis for fiae Degree of $41.5. MICBIGAN STATE UNWERSITY Theodore R. Efizerman 1964 LIBRARY Michigan State University THE EVALUATION OF THE BAUSCH AND LOMB REFLECTANCE SPECTROPHOTOMETER FOR THE COMPARISON OF MINUTE PAINT SPECIMENS BY Theodore R. Elzerman AN ABSTRACT OF A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE School of Police Administration and Public Safety 1964 APPROVED ‘Glljnfit’TTf—W Ralph‘E. Turner Chairmanj ,, *1 ' , ‘ [—{70'%"5; ’i'n - .. ‘L :1 6‘1’IV ‘ L1 . 5;. ‘IMembér) $7 1’) ...-.7 f ' I\ " \ifglr L’i‘ ,4 , r' N J.— .J ' ' (Member? ABSTRACT THE EVALUATION OF THE BAUSCH AND LOMB REFLECTANCE SPECTROPHOTOMETER FOR THE COMPARISON<3F MINUTE PAINT SPECIMENS by Theodore R. Elzerman Instrumentation is playing a very important part in the field of Forensic Science. The results of several sup— plementary tests of various properties showing similarities will make the comparison of evidence for purposes of estab— lishing positive identification more convincing as to probable source or origin. Paint and pigment specimens were measured in a wave- length range of 4OU to 700 millimicrons. The reflectance curves were recorded on a graph. Paint chip Specimens were mounted on white card stock with double stick scotch brand adhesive tape and examined in the reflectance sphere of a Bausch and Lomb Spectronic 505 Recording SpectrOphotometer. A Specimen covering an area of 40 square millimeters (approximately 6 x 7 milli- meters) of the illuminating beam was necessary to produce valid reflectance curves. Because a 40 square millimeter paint specimen is rarely encountered in the Forensic Science Laboratory, a procedure for diluting the paint speci- men with a white pigment-~lithopone-—was investigated. Using pure pigment smears, an area of 144 square milli- meters (12 millimeters square) was necessary in the path of Theodore R. Elzerman the illuminating beam to produce valid reflectance curves. Pigment and paint specimens diluted with lithopone and mixed with linseed oil or polyvinyl acetate as vehicles were smeared on glass slides. The specimens thus prepared were examined in the reflectance sphere of the spectrophotometer. The Spectronic 505 reflectance sphere has no value for directly examining paint chip specimens under 40 square millimeters in area. Diluting minute paint specimens with lithOpone, making smears on glass Slides and examining them in the reflectance sphere has limited value in the Forensic Science Laboratory. Concentrations of 0.1 per cent of a pure pigment mix, with a quantity of 10 milligrams of the mixture with lithopone as the diluent, were required for examination. Concentrations of 5 per cent of a light colored paint scraping and l per cent of a dark colored paint scraping with the same diluent required 10 milligrams of the mixture for examination. The paint specimen must be capable of being ground to a powder to produce repeatable results. Further, an area of 144 square millimeters with the diluted pigment and paint scrapings was required. A modification of the reflectance Sphere so that paint Specimens smaller than the above may be examined without treatment, such as by condensing the illuminating beam onto the specimen, may give this instrument more application to the comparison of minute paint specimens in the visible wave— length range 400 to 700 millimicrons. THE EVALUATION OF THE BAUSCH AND LOMB REFLECTANCE SPECTROPHOTOMETER FOR THE COMPARISON OF MINUTE PAINT SPECIMENS By Theodore R. Elzerman A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE School of Police Administration and Public Safety 1964 Q\ 1’ x, If ’3: ‘ ACKNOWLEDGMENTS I wish to thank Mr. Kendall Miller of the Truscon Paint Laboratories for a tour of the paint manufacturing operation and for securing the polyvinyl acetate and painted panels used in this study. Also, I wish to thank the Archer, Daniels, Midland Company for the pigment samples and the Minnesota Paint Company for the Lithopone sample used in this study. A Special note of thanks to Mr. Wilfred E. Dugas for the drawing of the Spectronic 505 Optical Schematic. I wish to express a most sincere thanks to my wife Liz for her assistance in the final writing of this thesis. ii CHAPTER I. II. III. IV. TABLE OF CONTENTS INTRODUCTION . . . . . . . . . . . . . . Sc0pe of the Problem . . . . . . . . Some Methods of Comparison and Identification . . . . . . . . . . History and Literature . . . . . . . . Purpose of the Paper . . . . . . . . . COLOR MEASUREMENT AND PAINT Color Measurement . . . . . . . . . . Paint . . . . THE SPECTROPHOTOMETER IN COLOR MEASUREMENT . The Spectrophotometer . . The Bausch and Lomb Spectronic 505 Recording SpectrOphotometer . Reflectance Measurements . . . . . . . . Reflectance Standard . . . . . . . . . . Standard Illuminants . . . Theory of Reflectance Measurements EXPERIMENTATION . . . . . Introduction . . . Reflectance Examination of Paint Chips Sample Preparation . Dilution and Examination of .Pure Pigments. Examination of Paint Scrapings SUMMARY . . . . . . . . . . . . . . Conclusions . . PrOposed Study . BIBLIOGRAPHY iii PAGE 00 \O \J-bl-d I-' l--‘ #4 rd F4 bah MMMt—‘H 04>me O\ (fi-DOJOOOJ (:0 OJ (.I'OQO‘W-"HnJ H 00“ 0100 0‘ \l TABLE I. II. LIST OF TABLES Automobile Paint Chips Examined . White Versus Black Backing iv PAGE 32 42 LIST OF FIGURES FIGURE PAGE 1. The Bausch and Lomb Spectronic 505 with Reflectance Sphere . . . . . . . . . . . . 16 2. The Optical Schematic of the Bausch and Lomb Spectronic 505 with Reflectance Sphere . . . . . . . . . . . . . . . . . . . . 17 03 A light beam passed into a sample of glass . . . 20 4. Diffuse Reflection Types . . . . . . . . . . . . 21 A. Specularly reflected . . . . . . . . . . . 21 B. Diffused reflection uniformly . . . . . . . 21 C. Part reflected specularly and part diffused 21 {3 0m \1 0‘01 5 00 Ml—‘é 'I. la F‘ F4 be #4 Fa la F4 Fa la ~o a) ~J (r w A o) no rd 0 2O 21 LIST OF GRAPHS Ragoon Red Reflectance Curves Oxford Blue Metallic Reflectance Curves Toluidine Red Reflectance Curves Chrome Orange—Hansa Orange Reflectance Curves Chrome Yellow Medium Reflectance Curves Chrome Green Light Reflectance Curves Ultramarine Blue Reflectance Curves Effect of White vs. Black Backing . Phthalo Blue G. Dilution Reflectance Curve Iron (C. P.) Blue Dilution Reflectance Curve Monarch Blue Dilution Reflectance Curve . Chrome Yellow (Med) Dilution Reflectance Curve Toluidine Yellow Dilution Reflectance Curve . Lithol Toner (Med) Dilution Reflectance Curve Toluidine Red Dilution Reflectance Curve Chrome Orange Dilution Reflectance Curve Chrome Green (Med) Dilution Reflectance Curve . Morocco Maroon Dilution Reflectance Curve . Weighed samples of pigment dilutions with linseed oil as vehicle (Toluidine Red-10%) Weighed samples of pigment dilutions with polyvin l—acetate as vehicle (Toluidine Red-10%) . Weighed samples of pigment dilutions with polyvinyl-acetate as vehicle (Toluidine Red-1%) vi PAGE 34 34 38 38 39 39 40 4o 45 45 46 46 47 47 49 49 50 50 52 52 53 GRAPH PAGE @. 22 Weighed samples of pigment dilutions with polyvinyl-acetate as vehicle (Toluidine Red‘Ool%) o o o o o o o o o o o o o o o o o o o 53 23 Paint specimen dilutions; red paint with polyvinyl-acetate as vehicle . . . . . . . . . 57 24 Paint Specimen dilutions; two Shades of green paint with polyvinyl-acetate as vehicle . . . . 57 25 Paint specimen dilutions; two shades of blue paint with polyvinyl-acetate as vehicle . . . . 58 26 Paint specimen dilutions; gray, yellow, orange and red undercoats 58 vii CHAPTER I INTRODUCTION I. SCOPE OF THE PROBLEM The fundamental problem of the forensic scientist is that of identifying an object which is held in evidence as having come from the same source as another object which is associated with a suspect. Paint fragments are frequently obtained as evidence in cases where physical force or contact has been made. Burglaries, hit-and-run accidents and even homicides may involve paint as evidence. In many cases the circumstances are such that the amount of evidence available for analysis is in the form of trace smears. With no standard quantity of paint to work with, methods of analysis and comparison will also vary, and any method which will give additional information will be useful. II. SOME METHODS OF COMPARISON AND IDENTIFICATION Only a few methods will offer absolute proof of origin. These methods include the fitting together of broken edges of paint chips or the matching of characteristic striated markings.l In some instances it is possible to identify the 1P. Kirk, Crime Inve ti ati n (New York: Interscience Publishers, Inc., 1960), p. 261. l 2 make, model and year of manufacture of a car by microscopic examination of its paint flakes.2 These situations are not often found in actual practice, and in most cases no single examination will give a positive identification of one specimen with another. It is possible, through several types of examinations, to show similarities which may prove the source or origin of paint chips or smears. The forensic scientist may conduct a visual or micro— scOpic examination to determine paint layers and colors,3 or density of the paint sample and pigment distribution.4 The paint sample may also be subject to micro- chemical,(5’ 6’ 7’ 8) spectrographic,(9’ 10’ ll) infrared 2c. F. Tippett, "The Identification of Make, Model and Year of Manufacture of a Car by an Examinat'on of its Paint Flakes," Medicinei Science and the Law, IV 1964), pp. 22-25. 3J. G. Brewer and-D. Q. Burd, "Paint Comparison, A Method for the Preparat1on of Cross Sections of Pa1nt Chips,’ ;. 2: Criminal Law and Criminology, xxxx (1949), p. 230. 4kirk, op. cit., pp. 688—690. 5F. Klug, O. Schubert, and L. L. Vagnena, "A Micro- chemical Procedure for Paint Chi Comparisons," Journal gf Forensic Science, IV (1959), p. 81. 6H. F. Payne, Organic Coating Techn lo , Volume II (New York: John Wiley & Sons, Inc., 19613, p. 870. . 7N. W. Hanson, "Analyses of Paints, Lacquers, and Varnlshes," Journal 9: the Oil and Colour Chemists' Associ- ation, xxxxl‘ll9sa7, p. 210. 8c. P. A. KOppelmeier, Editor, Chemical Analysis 21 Resin-Based Coatin Material (New York: Interscience Pub- isners, Inc., I958). 9Klug, Schubert, and Vagnana, 9p, cit., p. 95. 10W. A. Cregeen, "The Spectrographic Examination of Small Samples by a Procedure GivingOH1gh Sensitivity," Journal 9: Forensig Science, V (19 ), p. 226. 11C. E. O'Hara and J. W. Osterburg, An Introd cti n to Criminalistics (New York: The MacMillan C3., 1963;, p. 59B. 3 (12, 13, 14, 15) Spectrophotometric, or X-ray diffraction (16’ 17) examinations in determining its compositions and origin. Neutron activation analysis is also under investiga- tion and may prove to be a very important aid in the compari— son and identification of minute paint chips to determine their origin.(18’ 19’ 20’ 21) 12"Infrared Spectrosc0py. Its Use as an Analytical Tool in the Field of Paints and Coatings." Chicago Society for Paint Technology, 1960. 131. R. Harkins, J. T. Harris and o. D. Shreve, ”Identification of Pigments in Paint Products b Infrared Spectrosc0py," Analytical Chemistry, XXXI (1959 , p. 541. 14George L. Clark, Editor, The Encyclopedia g: S ctr sco (New York: Reinhold Publishing Corporation, 1960), p. 505. 15W. R. Heilman, "Nondestructive Infrared and X-Ray Diffraction Analyses of Paints and Plastics," Journal 9: Forensic Science, V (1960), p. 338. lélbig., p. 342. 17c. E. O'Hara and J. w. Osterburg, 22- cit., p. 620. 18V. P. Guinn and C. D. Wagner, "Instrumental Neutron Activation Analysis," nalytical Chemistry, XXXII (1960), p.317. 19D. Gibbons, "Activation Analysis-~An Aid to Forensic Investigation," Forensic Science Society Jgurnal, IV (1963), p. 33. 2OR. R. Ruch, et. al., "Neutron Activation Analysis in Scientific Crime Detection--Some Recent Developments," Journal g; Forensic Sciences, IX (1963), p. 119. 21A. K. Perkons, gt. al., "Further Development to Forensic Activation Analysis, Proceedin S g: the Canadian Society 9: Forensic Science, III (1964), p. 40. 4 With these thoughts in mind, reflectance spectro- photometry is evaluated as an additional method of compari- son for identifying paint specimens which might be recovered at a scene of a crime. III. HISTORY AND LITERATURE The fundamental way to measure the color belonging to an area is to break it down into its component spectral parts, the radiant flux from that area, and to measure each of these parts of flux separately.22 The spectrOphotometer is an instrument designed to measure the intensity of the light transmitted or reflected by a substance and, when pro- vided with an automatic recorder, a permanent record of the spectrum is rapidly obtained. Spectrophotometers have been found useful in examining physical evidence23 and one of the first Spectrophotometers which employed a recorder was the Hardy or General Electric Spectrophotometer.24 Since then, many recording Spectro- photometric instruments have become available. One of the more recent recording Spectrophotometers available is the Bausch & Lomb Spectronic 505. When this 22D. B. Judd, Colgr in Business, Science, and Industry (New York: John Wiley and Sons, Inc., 1952), p. 29. 23"Use of a Recording Spectrophotometer in the Exami- nation of Evidence," F.B,I. Law Enfgrcement Bulletin, XV (1946), p. 6. 24M. G. Mellon, Colgrimetry fgr Che ist (Columbus, Ohio: The G. Frederick Smith Chem. Co., 1945;, p. 72. instrument is equipped with a reflectance sphere it is capable of analyzing light reflected from an Opaque object from 400 to 700 millimicrons.25 The literature on the use of absorbance (or trans- mittance) spectrophotometry for qualitative and quantitative purposes is voluminous, but in contrast, there are few accounts of similar applications of reflectance spectro- photometry.26 Reflectance spectrophotometry has frequently been employed in industry for the descriptive evaluation of colorants and pigments.(27’ 28’ 29’ 3O: 31: 32: 33: 25Bausch and Lomb Bulletin on Specifications. Catalog Numbers D—2009, 0263., p. 10. 26H. Zeitlin and A. Niimoto, "Comparison of Transmit- tance and Reflectance Spectra of the 2, 4-Dinitr0phen 1hydra- zones of Acetone and 4-Meth l-2-pentanone," Analyticai Chemistry, XXXI (1959), p. 167. 27J. Sendroy and W. C. Granville, "Application of Reflectance SpectrophotometrK to Quantimmive Mi roanalgsis," Industrial and Engineering C emistry, XIX (1947 , p. 5 0. 28Committee on Colorimetry, Optical Society of America The Science 9: Color (New York: Thomas Y. Crowe 1 Co., 1953) p. 218. 29H. A. Gardner and G. S. Sward, Paint, Varnishes, Lacquers, and Colors, (Twelfth edition; Bethesda, Maryland: Gardner Laboratories, Inc. 1952) p. 13. 30D B Judd c 19 ° B ' s ' ry . . , o r in us1ness, olence and Indust (New York: John Wiley and Sons, Inc., 1952) p. 8 . . 31D. R. Duncan, "The Identification and Estimation of Pigments in Plgmented Compositions by Reflectance Spectro-_ photometry," Journal 9f t e 011 and olour Chem1§ts A55001— ation, XXXXV (1962) p. 300. . 32G. Reimann, D, B. Judd, H..J. Hiegan, "Spectrgphoto- TCCAlStang Cglgrimetglc Detegmlnationfoih he Soloisso .the an ar 0 or ar 5, ourna g_ e 99 1ca oc1e y of America, XXXVI (1946 p. 128. 33K..L. Kelley K. Gibson and D. Nickerson "Tristimu- 1fistSpeg1f1c§tlons of thenMunselllBogk fif Color irgm Spectro- p o ome ric easuremen s Journa g_ t e thica ociety 2f America, XXXIII (1943) p. 355. 6 34' 35) It also has been used to study coba1t(II) salts36 37 mecuric iodide and other reactions resulting in the pro- 38 (39, 4o, 41) duction of color or the changing of colors. The examination of paints and other pigmented composi- tions by reflectance spectrophotometry has been studied by 1.42 Duncan in detai While some workers feel that informa— tion which may be derived from reflectance curves without interpretation by means of color theory is limited, although (43, 44) in some cases valuable, others believe that no further 34Mellon, Op, cit., p. 104. 35c. A. Lermond and L. 8. Rogers, "Differential Measurements of Reflectance," Analytical Chemistry, XXVII (1955) p. 340. 361. I. Katzin, "Reflection Spectra of Some Solid Cobalt (II) Salts in the Visible Re ion," Journal 9f the American Chemical Society, LXXV (19533, p. 2830. 37G. Kortum, "DiffueaReflectance Spectra of Mercuric Iodide on Different Adsorbents," Transactions 9: the Faraday Society, LVIII (1962) p. 1624. 38Sendroy and Granville, Qp, cit. 39I. R. Griffiths, K. Latt, M. Symons, "Diffuse Reflect- ance Spectrophotometry in the Ultraviolet Using Powdered Salts," Analytical Chemistry, XXXI (1959). p. 1338. 4OS. Wendlandt, et al., "High Temperature Diffuse Reflectance Spectroscopy," Analytical Chemistry XXXV (1963), p. 105. 41W. Wendlandt, "The Dynamic Reflectance Spectro- scopy," Scienge, Vol. 140 (1963), p. 1085. 42Duncan, Op, cit., p. 305. 43E. Atherton and D. Touch, "ASpects of Colorimetry Applied to the Colour Gamut of Pigments," Journ 1 pi Oil and Colgur Chemists' Association, XXXX (1957), p. 115. 44Duncan, 9p, cit., p. 300. reduction of Spectrophotometric data is necessary if two objects have identical curves for given angular conditions of illumination and view.(45’ 46) Paint comparison in the forensic science field has been done utilizing reflectance data with the Beckman Model B. Spectrophotometer.47 The instrument can handle a paint chip that is 3.2 by 4.8 millimeters (15.4 sq. millimeters), and can examine it in a wave length range from 350 millimicrons to 1000 millimicrons. In most instances the quantity of paint encountered is smaller than this and more often is nothing more than a smear. IV. PURPOSE OF THE PAPER In relation to color, the chief problem of the foren- sic scientist is the matching of colors. A procedure of matching colors from a collection of samples of various colored materials is unsatisfactory because of the inconsis— tency of the color of the sample due to aging.48 Also, color sense varies with the individual and is influenced by other 45Judd, op, cit., p. 94. 46W. F. Ulrich, F. Kelley, and D. C. Nelson, "Evalu- ation of Colorants by Spectrophotometric Methods," Paint Industry Ma azine, LXXIV (1959) p. 15. 47J. F. Williams, "Examination of Paint Chips and Scrapings with the Spectral Photometer," Journal f Criminal Law, Criminglggy and Police Science, XXXXIV (1954 , 647. 48"Reflectance Attachments Provide Data for Precise Calculation of Tristimulus Color Values," Beckman Appli a- tign Data Sheet QKE78-MI. Beckman Instruments, Inc., Fullerton, California. 8 factors, such as the field surrounding the sample and the manner of observation.(49’ 50) Color matching will vary too, with the quality of the light by which the comparison is made and the angle at which the samples are viewed with respect to the sample and illumination.51 A method of objectively matching and specifying colors which overcomes the above problems involves the use of the spectrophoto- meter(52, 53, 54) The reflectance sphere on the Bausch and Lomb Spectronic 505 Recording Spectrophotometer is evaluated as a means of comparing and identifying minute paint chips and paint scrapings which may be encountered by the forensic scientist. Results of such tests could be used to supple- ment visual, micrOSCOpic, chemical and spectrographic examinations to Show similarity or dissimilarity of color as well as composition. 49Atherton and Tough, Qp, cit. , 50E. A. Zahn, Scientific Paint Evaluation (Dayton, Ohio: Research Press, Inc., 1955), p. 265. 51E. I. Stearns, "Spectrophotometry and the Colorest," American Dyestuff Reporter, Vol. 33 (1944), p. 18. 52Duncan, gp. cit., p. 300. 53Judd, op, cit., p. 82. 54Max Saltzman, "Color Matching via Pigment Identifi- cation," yestuffs, XXXXIII (1959), 57. III|||II|I|II I!!!) II) I CHAPTER II COLOR MEASUREMENT AND PAINT I. COLOR MEASUREMENT Substances are colored because of their selective absorption of white light. If absorption occurs uniformly at all wavelengths, the object appears to be gray or black. If the absorption is non—uniform, that is, if absorption is more pronounced at some wavelengths than at others, colors are perceived which are complimentary of those repre- sentative of the absorbed wavelengths.(l’ 2) The physical basis of color can be demonstrated by passing separate beams of white, red, green, and blue light through individual red, green, and blue filters. The red filter allows the red portion of the white beam and the red beam to be transmitted. The green filter allows the green portion of the white beam and the green beam to be trans- mitted. The blue filter allows the blue portion of the white beam and the blue beam to be transmitted. This may also be demonstrated by superpositioning yellow, magenta and cyan glasses which are employed in the printing of colored 1W. F. Ulrich, F. Kelley and D. C. Nelson, "Evaluation of Colorants by Spectro hotometric Methods," Paint Industry Magazine, Vol. 74 (1959 , p. 11. 2H. F. Payne, Organic Coating Technology (Volume II; New York: John Wiley & Sons, Inc., 1961), p. 695. 9 10 photographs. This phenomenon is illustrated in many articles.(3’ 4) Colored reflecting materials make selection from the spectrum in substantially the same manner. Colored materials rarely absorb or reflect all of any wave length that may fall upon them. The per cent reflectance for all wave lengths of the visible spectrum needs to be known for the measurement of the color of any object. The reflectance spectrophoto- meter is used for this purpose. The wavelengths of maxima and minima reflectances on Spectrophotometric curves are highly characteristic of the materials of which the sample is composed. Such data on wavelengths is valuable for analysis and identification of paint Specimens. The visible spectrum is only a small part of the entire electromagnetic spectrum. It is the portion of the Spectrum between 400 and 700 millimicrons. This is the portion of the spectrum for which the reflectance measurements in this report are made. II. PAINT Paint is defined in the ASTM Standards as "A pig— mented liquid composition which is converted to an opaque solid film after application as a thin layer."5 A pigment 3Committee on Colorimetr , Optical Society of America, The Science of Color New York: Thomas Y. Crowell Co., 1953), p. 220. 4w. D. Morgan, editor, The Enc 1 ed'a of Pho p- graphy (New York: Greystone Press, 1963), p. 802. 5A. S. I. M. Standards 1261. Part no. 8, Designa- tion D16-59. 11 is defined as "The fine solid particles used in the prepa- ration of paint, and substantially insoluble in the vehicle. The vehicle is the entire liquid portion of a paint which includes the pigment, binder or film-former, voltaile sol- vent, and anything that is dissolved in the liquid portion.6 Color and opacity in paints are imparted by the pig— ment, but it should also be noted that some pigments are not used to impart color or opacity but are merely extenders. Pigmented paints are formulated from a wide variety of materials and have a broad range in usage. Consisting essentially of a pigment and vehicle, the paint's character- istics and functions are thus determined. Pigmented coatings include house paints, industrial automotive paints, red-lead paints, aluminum paints, colored lacquers, and water paints, as well as certain specialized products such as vinyl resin paints. A wide variety of pigmented paints have been formu- lated to suit specific purposes. The vehicle that is most suitable for an outside wood paint is not desirable for an interior paint. Fade—resistant pigments are used in finish paints for machinery, while rust-inhibiting pigments are used in the priming paint. A gloss or semi-gloss paint is needed for walls and woodwork in kitchens, because of better washability, but a flat finish is usually desired for living room walls. 6Payne, op. git., p. 677. l2 Pigments may be classified as natural and synthetic and in each of these groups there are organic and inorganic types. There are hundreds of different types and makes, some of which will be described.(7’ 8’ 9) Lead and zinc are terms frequently applied to paint pigments. In usage, they do not necessarily denote pulver-' ized metals, but chemical compounds of the metals, such as lead carbonate, lead sulfate and zinc oxide. White lead is either basic lead carbonate or basic lead sulfate, or a combination of the two. Red lead, which is used in metal priming paint, is one of the lead oxides. Titanium indi— cates a pigment containing titanium dioxide and lithopone contains zinc sulfide. These are all inorganic pigments, as are prussian blue, chrome green, zinc yellow, and the siennas, umbers and ochres. Synthetic organic pigments include the toluidines in reds and yellows, and the phthalocyanines in blues and greens. Originally pigments were employed solely to impart color but now they are recognized as influencing many other properties of paint. Pigments are mixed to achieve differ— ent colors. Also to be considered are their effects on 7Paint Manual. United States Department of the Inter- ior, U. 8. Government Printing Office, 1961, 2nd Ed. 8H. Gaertner, "Modern Chemistry of Organic Pigments," Journal cf the Oil and Colour Chemists' Association, XXXXVI (1963), p. 14. 9George L. Clark, Editor, The Encyclopedia 9f S ectro- scgpyé (New York: Reinhold Publishing Corporation, 1960), p. 51 . 13 hiding power, settling, workability, stability after exposure and ability to protect organic vehicle binders from the damaging rays of sunlight. Most pigmented paints contain mineral fillers known as extenders. These are white or colorless pigments of low opacity. They contribute little to hiding power but because they are generally high in oil absorption properties, they act to minimize settling of pigments. They help control gloss and working consistency. Extenders used are magnesium silicate, barium sulfate, blanc fixe, barium carbonate, kaolin, calcium carbonate, diatomaceous silica and mica. The amount of pigment in paint varies from as low as 10 per cent by weight in some vinyl resin paints to 80 per cent in some red-lead-in-oil-paints. House paints contain from 60 to 70 per cent pigment. The pigment content influences the gloss or Shine of a dried paint film. Gener— ally, the lower the pigment content, the higher the gloss. The vehicle portion of the paint contains both volatile and non-volatile constituents, and is actually the film—forming part of paint. The volatile constituent facilitates the application and drying of the paint, but has no permanent part in the dried paint film. The non-volatile constituent is the binder, being an integral part of the paint film which binds the pigment particles together and insures adhesion of the film to a surface. The non—volatiles are substances such as linseed oil, vinyl resin, alkyd resin, nitrocellulose, and the synthetic resins of phenolic, epoxy, chlorinated rubber and various hydrocaron polymers. CHAPTER III THE SPECTROPHOTOMETER IN COLOR MEASUREMENT I. THE SPECTROPHOTOMETER The SpectrOphotometer provides a precise measurement of the absorption or reflectance process at different wave- lengths and can be employed to determine which portions of white light are absorbed by a substance and to what extent. In many instances it serves as a replacement for the human eye. It is valuable in the elimination of errors caused by the differing color responses of the human eye in various individuals. This instrument also detects metamerism and can perform a precise comparison faster than the human eye.1 The Spectrophotometer has several advantages over a colorimeter, which can also be used to measure reflectance. The essential difference between colorimetric and spectro- photometric measurement of color is the number of divisions into which the Spectrum is divided when making reflectance or transmission measurements. Instead of three broad regions covered by the blue, green, and amber filters, the Spectrophotometer uses narrow bands over the entire visible Spectrum.2 The sample may be scanned in a few minutes and 1W. F. Ulrich, F. Kelley and D. C. Nelson, "Evaluation of Colorants by Spectrophotometric Methods," Paint Industry Magazine, Vol. 74 (1959), p. 12. 2H. F. Payne, Organic Coating Techn 1 (Vol. II; New York; John Wiley & Sons, Inc., 1961), p. 695. 14 15 a permanent reflectance spectrum recorded on a chart when a recorder is attached to the spectrophotometer. The essential parts of the Spectrophotometer include a light source, a prism or a grating to produce successive wave bands, a standard reflecting surface, and a receptor. These will be covered in more detail in the following dis- cussion of the Spectronic 505. II. THE BAUSCH AND LOMB SPECTRONIC 505 RECORDING SPECTROPHOTOMETER The Bausch and Lomb Spectronic 505 Recording Spectro- photometer is capable of automatically recording spectra in the ultraviolet and visible wave lengths. When a reflectance Sphere is attached to the instrument, it is limited to a wave length range of 400 to 700 millimicrons. The Spectronic 505 with reflectance Sphere as employed in this study is shown in Figure l. The Optical Schematic is illustrated in Figure 2. The Spectronic 505 employs a light from a standard tungsten source (Source C) which is described in Section V. The beam is passed through a monochromator which uses two gratings and two sets of fixed slits set at five milli- microns. The beam then passes into a beam splitter. This provides two separate light paths, one for the sample and one for the reference. The beams pass into the reflectance Sphere, one beam reflecting off the sample and one beam off the standard reference. 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A slight minimum between 470 and 520 millimicrons as well as the maximum between 520 and 610 millimicrons is not present in curve 4 for the 20 square millimeter sample. Though curve 4 as well as curve 3,for a 9 square millimeter sample, reflect less than 90 per cent of the illuminating beam, no valid data is present. Thus a Specimen which would fill the illuminating beam in excess of 30 square millimeters would be required here also. The solid paint chips used in Graphs l and 2 were whole chips cut to fill the illumination beam with 225 square millimeters of solid specimen while the samples were small chips placed on the adhesive portion of the tape to fill the illuminating beam to the areas indicated. The small Spacings between each paint chip would have the effect of varying particle size resulting in deviations of the reflectance curves.3 Inspections of these reflectance curves as well as the other 14 paint specimen reflectance curves thus examined, revealed that when the illuminating beam area was covered with 40 square millimeters of paint specimen in the Bausch and Lomb Spectronic 505 Reflectance Sphere, valid curves for com- parison purposes were received. As a 40 square millimeter specimen of paint is rarely encountered in the Forensic Science laboratory, an 3C. A. Lermond and L. B. Rogers, "Differential Measure- ments of Reflectance," Analytical Chemistry, Vol. 27 (1955), p. 346. 36 investigation was made to determine just what specimen size could be adequately analyzed with the reflectance Sphere by diluting the specimen with a white pigment to cover a larger area of the illuminating beam in the reflectance sphere and thus obtain reflectance curves suitable for comparison. III. SAMPLE PREPARATION In this examination pure pigment smears were prepared using the pigment and linseed oil to determine the optimum area to be examined by the illuminating beam. The pure pigments used were secured from a pigment manufacturer and are those used in the manufacture of commercial paints. A simple technique for preparation of small uniform paint smears was used.4 This consisted of placing a piece of adhesive latex tape on a one inch by three inch glass slide, and cutting out a window of the desired size. The pigment—linseed oil mix was then Spread out by drawing a glass slide over the window at a 45 degree angle. The angle, the speed of drawing, and the number of times the slide was drawn across was kept constant. After drying, the tape was removed from the slide, leaving the pigment film. To prepare the pigment for this operation, fifty milligrams of pigment were placed in a mortar and moistened 4H. Barnes and E. T. White, "A Simple and Inexpensive Technique for the Preparation of Small Uniform Areas of Paint Films of Graded Thickness," Journal 9f 9;; and Colgur Chemists' Association, XXXI (1948), 470. 37 with sufficient linseed oil to make a blend mobile enough to smear. The amount of linseed oil varied with each pigment because some pigments required more to moisten them. How- ever, each in the series of smears for a particular pigment— linseed oil mix was of the same concentration because each series was prepared from one batch of mix. Enough of this mix was used in each window to cover it with a dried film 0.11 millimeters thick. Five pigments were examined in this manner using a window size of 6 millimeters square, 8 millimeters square, 12 millimeters square, and 16 millimeters square. The refer- ence used in this series was a block of magnesium carbonate. The background used behind the pigment smear on the glass slide was also a block of magnesium carbonate. The results are illustrated in Graphs 3 through 7. In all five cases there was considerable difference in the per cent reflectance between the 12 and 8 millimeter sized windows. The increased difference in reflectance between the 12 and 8 millimeter sized windows was caused by the increased area of specimen being illuminated by the beam. The per cent reflectance increased when the specimen size was smaller than 12 millimeters square because of the increased blank area (reference) being illuminated behind the Specimen. Because of this, a 12 millimeters square (144 Square milli- meters) Specimen area was chosen as the Size for preparing diluted samples to be compared. Of interest also was whether a white or a black -‘-- -. —--..-.---u -.-- .-- .- It I Z + CFIIAYO - 'sAMh! M“ l I 1 out 0090 tons \uuuuom “not w rucum coo. GRAPH 3 0.... O O... I-ouuvoougu ‘ RAPH 4 F GRAPH 6 uno- noon n-Ih ont- SC!- 000. u a o vacuum mm m. mam 4 aha .\\I‘l\§ .t‘I , . Zqu><3 -.I.“ l\‘~n\ 385?...3 ‘ ,zs.:s?§uaqsi. so ... :23 T . . A . . H .. M f . ‘ a . -1-.. .--._-.-,.‘;A ..-.“- . ‘ a v i-.+--._..v--_.._-._.“ u n . ._ I . .... H xi.-. ......vi ... u . ... . . ... . IIOIOIOI .....,. t- . . , . A 4 . . Y ~ --r»—--o-w"“ O . . . . --« 1 A . . ..v-.. ..-.(..... I up -.--,W < 3 J BAUSCH ‘ LOMB '"CORPORAHLU ,- gAIALUu \g. gi-‘u-d.‘ .‘,_' 1." 4. 1.--,> . > ' .. .....e 2" ‘“U“’)Iul 1 I 70-.l . .7 . V ‘ J . l - , -__.,-.2- . , .. 1 . I Z ’ 1 ‘ —§--—-0——- ., -7. ~vv¢ b t n . “k? PIICINI . ‘ wunmcm IANGE m PERCENT I I o----v- Q I I o I I V U ----.----..._. , I I l I '0 ' o I .-.—.----.-- O --\ I ~| . I \ I I l I ,. ‘ a o I . I I I I -..-..-.-....¢---- .. ,., v \ I I ....'.... ..-... I ,. I. -- ---§--—-- I 3 f ....-. 4 . . X . I --.-.--..4- . 4 .r"d ..-.-. .......---.---.... I l ..--..ro.» I I, I I .--.,.--. I l I D I --. I O I I. 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O I . I I - I Ilsa; waveuuom “not w 90ch ---.¢.---.....‘ 0 I I O 'IICINI I -...,... .-..o... I | I 0 I o I I I O o . o I O O O O I In" mom nuqa I 3---. I I I I 0 I ~-9---..--- 47 .Au.°u I DO.” lIIUUlIl'UnnAI-u 2.3.: i 324. fox-=2; a .. . blow-us I3 GRAPH i..§: . .2 OH h . 1 .3 x ”2.: 9 To“ ...-9 L tA‘ u¢.I .n. 64 .--...YQ- .. T H ..1- M H- ... . 1.. N... .... .... 1, H H . . H . . Hun,......H.1.....H “H r.t'..:v|t¢ .. v ...IIL VOuOrOLTb-on. at- «I?! . MH . , . . . ..H .. .H . 1 . . 1L45-i.o..‘f~.t .” AVOO-vb-AIHYOICIfb H LI H H . . L. in?“ T; 1 .H H .1 .- .... ... . ... H... ...H- .---.I.-1I..1T:I1 - Hf. . . ....H 27.; H H/.. H 1.. ”it” 5”...” y -11.; ...-..1-IFKYJJ : .. ..... H . _ .. 1 .. . .. H . H H . .. .. .. . .. . n u H h r. g H. H .H .. ..o.~..¢.n..o. . . _ . . ...1 .. ... .... .. . . . . .. . >. ... .... - H . H ... . .. 1 . .. ... . v _ . ... ... .... _ _ _ . ... ... .. . H H . 1 . ... .. . .... w H H h . ... f. . .... . 0.. I. I l5 GRAPH 7H7,H.HY,--..,1.H-.HH'-H,H---,-----yp-H..H.....»a -.—.....-------H._-.-.-H-.-_-_l ---d . 1 « . o 9331 .Ilovlvo o . . oix‘tV nut; n .Hd .H... . m ii.‘ to Aft. Av- l .... an .vOchn .. , _ H . _ Y . . .. .. . ._ . - u - o _ . .1 .. . . .c o H ... _ _ ... “I H . v.. v a . ’- ova.. .. s..> -.. .I.nl.o’V:.l. 6:4. Tb|u v... .... 1 ./ H .. . Ii .. H . .... _ r . H . ”unw1 H H 1 ~‘.¢1 H / H _. H ,. , .3.- . ... o .. ... ...o _ .. -0- or ..).....1 -ootlv’riv . .. . 1 . . . .. ..... u 1 . .1; . . H‘ H _ Ar . .unni H . . . . . . v? . 1o. ... . .. «In 1 q... ...!o.. ...-9v «at-i1 a... H . H ._ ooii _ . H . i .H.... H ””H.1 . 1 . . I. u I in y > . :I nfitv vhnuvnnut -‘n‘AVI. u‘ll -VIFAVI‘VI O..- H J u p .U .... ... 1 .1 1 H 1. H . H ... ...H .. . ..v. .... . - ......... ...-9.-.. -. ..-. $.4- --. ...H O H1 _ o .s 1 H a u- .u . .... nit. .. u . — v »v . u p I... v... 66 “A . .5 H_ h H H H g .H... 33. . .... . . ...»- .......r> . A ~. 0c..Y~Vu u... L ....A H. . ..H _ . .. . .. . _ H. .. H H . .. . ... . . .... . H l H. H . _ . .. . . ob . .. _ _- .1 H _ . . .. .... < v. H ... .7 .H. . fl . .. . .. ... ...»??Yb .... . .1 l _ . _ . . . _ 4 Hr . H _ . .. . . 1 . . H. H _ . . .. . . _ 1 -_ _ _ H - 1 .. . . . w v I. . . . ..¢. .. no.. to. nut-AVODVvAvOAOI . . . . . . . .u -. .. . .... _ fl a. H . . .. . . .. ..... . .. . . H ; . 11..A . 1 . . 1 . . .. .. . .1 _ m u H . .7 M. Mr.“ . . l , - _ _ . . . ... U . ..h H H r ... . ..... .... ....1 . . - H. H HH . H ... . . .H . ... .... _ _ H .. 1 . ... .... . .1 . ’1 v I... . . .l/ o o ’H . H. 1. v. v... .-n¢ ... ...- . . 1 . ... .. . ,1. H H “.HH tH . H. .9 c I..- H H . A uoyYOi9 .... 0..» _ 1 . ._ _ .. o .... . 1 . . .o . .... H .. . .. . a... r r > . . ...» . - I6 GRAPH I .1 9...-.HH «+-~Q.~. .- I H U C U ‘ a U 0 I ‘ C 2 .- O 2 . cl - > < 3 wwuluom nun! my. menu 51 Toluidine Red pigment diluted to 10 per cent with lithopone and mixed with linseed oil. The repeatability of the curves is due to the uniform thickness and complete coverage of the window area. Slight variations are due to surface texture and particle size, rather than the quantity of specimen used. Another vehicle was investigated to be used in place of the linseed oil. This vehicle is a copolymer of poly— vinyl acetate. Graphs 20 through 22 illustrate the curves of weighed duplicate samples of three concentrations (10 per cent, 1 per cent, and 0.1 per cent) of a Touidine Red pigment mixed with poly—vinyl acetate as the vehicle. Again, good repeatability is demonstrated at the three con- centrations. Comparison of curves 3 and 4 on graphs l9 and 20 shows that linseed oil has much more absorption in the low wave length regions than does polyvinyl acetate. This does not affect the reflectance curves of pigment specimens which are dark in color, but would have an effect on the reflectance cuves of pigments which give a high percentage of reflectance at the low wave lengths. This results in a masking effect which would be overcome by using the vehicle- lithopone mixture on a glass slide with the same window size in the reference beam. The effect of dilution is a measure of the reflectance of the components present in the pigment sample. The dilu- tion causes a change in reflectance because the coefficient of scatter of the paint changes with wavelength and is Ito-soon." an r N“ .. 2 u U I u t g 'wavl and" “no: GRAPH ' '4‘?” -1 I. I“ 7' 0AM BAIL van-main unalmruccm W | RAPH 20 GRAPH 2| GRAPH 22 h 2 IO U a In ‘ I O I ( I 8 .- 0 8 C d C O wanuuom autumn-um m ‘ Lv—f—a- 54 affected mainly by the predominant pigmentll (which is white in the case of dilution). Particle size also affects the reflectance curve. A decrease in particle size will in- crease the intensity of the reflectance curve,(l2’ 13) with the region of the reflectance maximum being most pronounced. In Graph 22 the greater variations of curves 5 and 6 are due to the poor coverage of the window area. The polyvinyl acetate vehicle was found to be much easier to work with. This vehicle dried in the air in a matter of minutes while linseed oil required more than a week to dry. 'The specimens prepared with polyvinyl acetate were non-glossy, whereas those, particularly in colored pigment of dark colors, made with linseed oil were glossy. When working with polyvinyl acetate, the equipment was readily cleaned with water, while working with linseed oil, organic solvents were necessary in cleaning. It was found that concentrations of less than 0.1 per cent of a pure pigment should not be used. The minimum quantity of mixture for a pigment dilution of 0.1 per cent should not be less than 10 milligrams to insure proper coverage of the window area 12 millimeters square (144 square millimeters), and to produce repeatable curves. llIbid., lzIbid., p. 305. G. Kortum, "Diffuse Reflectance Spectra of Mercuric Iodide on Different Adsorbents," Transactions g; the Faraday Society, Vol. 58 (1962), p. 1625. 55 IV. EXAMINATION OF PAINT SCRAPINGS In this section of the study, actual paint samples were ground and mixed with lithopone to test the proposed method of examining minute paint specimens with the Spectronic 505 with reflectance sphere. Twelve painted panels, consisting of single layer automobile undercoats and finishes, were secured. These single layer samples eliminated the necessity of separating multi-layers of paint which would be commonly encountered. The panels were prepared by a paint manufacturer to determine paint flowing quality and no information was available about the pigment composition of the paint. Five milligram and one milligram samples were scraped from the panels and mixed with lithopone to give five and one per cent dilutions. (A maximum sample of five milli- grams of paint scrapings was used because larger amounts are rarely encountered by the forensic scientist, and could be compared directly as described in Section II earlier in this chapter.) An attempt was made to grind the scrapings in a Wig—L-Bug Grinder-Mixer but met with limited success until lithopone was added. The lithopone apparently provided enough body to the mix to give a good grinding action. Ten milligrams of the paint scraping-lithopone mixture were placed on a glass slide and wet with one drop of polyvinyl acetate. This blend was smeared to cover a window 56 12 millimeters square in area on the slide and allowed to dry. All samples in this section were prepared in this manner. These samples were examined in the reflectance sphere, using a 12 millimeters square smear of lithopone-polyvinyl acetate in the reference beam. A magnesium carbonate block was used behind the glass slides in both the sample and reference beams. - To illustrate the difference between diluted and un- diluted paints used in this portion of the study a reflect— ance curve of each painted panel, masked with white card stock to expose a 12 millimeters square to the illuminating beam, was made. White card stock with a 12 millimeters square exposing the magnesium carbonate was used in the reference beam. Although a 40 square millimeters area gives valid curves for comparison of undiluted paint specimens (see Section II earlier in this chapter), a 12 millimeters square area was used in this part of the study to keep the illumi— nated area constant in both diluted and the painted panels. Some of the reflectance curves are illustrated in Graphs 23 through 26. Curve 3 in Graph 23 is that of the masked blank before correction of the 100 per cent line with the optical density control. The 100 per cent line had to be rechecked between each run employing lithopone-polyvinyl acetate in the refer- ence beam and the masked magnesium carbonate in the reference PIICINI PIICINI . RAHd 23 GRAPH 24 .- 2 U U I - ‘ WAVIIINOHI IANOI o 0 z ‘ c 8 h o 2 u g ‘ ’ bk“ . ‘O~---.~-. v v . --HHH---.._. .+..--‘.. 4 . n O o o.H n :- .; :- l . ..I ...-..---....-.H..-4 ,-. I c 1.. o D ‘ n o i l .--...---...-- O'IlAYOI §A§\_HGI ! I I O wavuauom nus! m nncmt 3 O- :3 ‘~ oi: IH‘( Own 4 .. Z n ..v. u _--H- .. H -H-HH U . .... . .. . a O . U i Q. ‘P 'I Q 5 . I -H-+'H-H.- -A ' ' I’. I .3: 6 1" ' -1-HH.-.1-.--1_‘_-1H " . ' I I -l o ' Z ‘ - I h 0 2 u —l U > ( 3 GRAPH 26 ‘ ——— 59 beam. This was necessary because the area illuminated outside of the lithopone—polyvinyl acetate in the reference beam was reflected from the magnesium carbonate block behind the glass slide. In the case of the masked magnesium carbonate in the reference beam, the area outside the 12 millimeters square was reflected from the card stock. (The illuminating beam size is approximately 16 x 19 millimeters.) 'The card stock has different reflectance qualities than does the magnesium carbonate. Curves 5 and 6 of Graph 23 represent two separate pre— parations of a 5 per cent mixture of red paint scrapings and lithopone. The repeatability is poor, although the two have the same general curve. The l per cent paint-lithOpone mix as represented by curve 4 may still be of value because there is a broad minimum between 480 and 510 millimicrons which indicates some absorption in the blue—green wavelength region. Graph 24 illustrates the reflectance curves of two shades of green. Curves 4 and 5 represent two separate pre— parations of the 5 per cent paint-lithopone mix but again repeatability is lacking, although they do possess the same general curve across the wavelength scanned. It is also noted that the diluted specimens reflect the same general type of curves as do the masked paint panels from which the specimens were removed. Two shades of blue are illustrated by the reflectance curves in Graph 25. Here curves 5 and 6 reflect much better 60 repeatability indicating better grinding and mixing of the paint specimen with the lithopone. Curve 4, illustrating the reflectance of a l per cent paint-lithopone mix, is lacking in detail in the low wavelength region. Curves 3 through 5 illustrate that 5 per cent dilu- tions of the paint Specimens shown in curves 8 through 10, give valid reflectance curves. Curve 2 illustrates that dilution of a gray paint produces a straight reflectance curve, similar to the undiluted paint (Curve 7). The per cent reflectance is dependent upon the shade of gray. Otherhsamples were examined using a one per cent dilu— tion but the reflectance curves are not included here because the reflectance was greater than 90 per cent and approached the reflectance of the blank. If a light colored paint sample is diluted to less than five per cent with lithopone, it will not produce a valid reflectance curve. Therefore, the smallest amount of a light colored paint which could be validly examined by this method would be a l milligram sample (1 milligram paint and 19 milligrams lithopone to give a quantity of 5 per cent dilution which can be ground and mixed to recover the 10 mil— ligrams necessary to cover a 12 millimeters square area). Dark colored paint samples could be diluted to one per cent with lithopone and still produce a valid reflectance curve. Theoretically a dark paint sample weighing 0.2 milli- gram could be examined. Due to the mechanical limitations described below, this was not done. 61 Microsc0pic examination of the diluted paint smears showed that the grinding of the paint Specimens was not uniform and in some cases, minute particles of paint, rather than a complete powder sample, were observed. The particle size of the paint and the lack of uniformity of the smear on the glass slide would have an effect on the repeatability of reflectance curves from individually prepared specimens because they affect the coefficient of absorption.(l4’ 15) Additional samples were subjected to grinding with lithopone in the Wig-L-Bug for varying times. It was found that the paint specimens which were brittle, ground to a powder and produced an acceptable smear such as is illus— trated in curves 5 and 6 of Graph 25. Paint which was somewhat soft and flexible did not grind to a powder and the smears made from these Specimens were not acceptable because of the varying sized paint particles present. Another problem is presented by multilayered paint Specimens. Mechanical separation of paint layers is possible if they are not damaged or smeared. Because of the small— ness of the paint specimens generally handled in the forensic science laboratory, mechanical separation of paint layers is impractical. Selective solvent separation was also investigated. Although solvent separation of paint layers is acceptable in l4Duncan, op, cit., p. 305. l5Lermond and Rogers, op. cit., p. 343. 1 62 some cases, again the small Specimen size is a limiting factor because of the tendency of the solvent to creep during evaporation resulting in a loss of the paint Speci— men. Relatively large paint specimens would be required for both mechanical separation of layers and a selective solvent procedure. Specimens sufficiently large for these two pro- cedures could be examined by the method described under Section II earlier in this chapter. CHAPTER V SUMMARY I. CONCLUSIONS Several items should be considered before reaching any conclusions from the viewing of reflectance curves. No quantitative results Should be attempted directly from reflectance curves of paint Specimens. A mathematical interpretation, such as proposed by Duncan,1 Should be used for quantitative results. However, the wave lengths for maxima and minima of the curves Should be Similar for like Specimens and are of value for qualitative measurements.2 It is doubtful if these curves could be compared with known standards to identify the brand or manufacturer of the paint because of the unknown degrees of weathering to which the evidence Specimens have been exposed.3 It is common know- ledge that if two panels are painted with the same paint and one panel is subjected to all weather conditions, a differ- ence does occur because of the weathering. No examination 1D. R. Duncan, "The Identification and Estimation of Pigments in Pigmented_Compositions by Reflectance Spectro- photometry," Journal 9: the Oil and Colour Chemists' Asso— ciation, xxxxv (1962), 300. 2D. B. Judd, Color in Business, Science and Industry (New York: John Wiley and Sons, Inc., 1952), p. 94. 3J. F. Williams, "Examination of Paint Chips and Scrapings with the Spectrophotometer," Journal 9: Criminal Law, Criminology, and Police Science, Vol. 44 (1954), p. 647. 63 64 of the weathering effect was made in this study. In conducting reflectance measurement examinations, each case must be studied separately on its own merits, as well as running a number of controls. This, of course, is nothing new to the forensic scientist, as controls and blanks are required in most of the examinations in this field. In this study, the reflectance Sphere of the Bausch and Lomb Spectronic 505 Spectrophotometer in the wave length range of 400 to 700 millimicrons was evaluated for comparing minute paint Specimens. The Sphere would require paint chips covering an area of 40 square millimeters of the illu— minating beam to produce valid reflectance curves. Because a 40 square millimeter Specimen is rarely encountered in the Forensic Science Laboratory, a procedure for diluting the paint specimens with a white pigment and examining a smear, made on a glass Slide, with the reflectance sphere was investigated. Examining pure pigment Specimen smears Showed that an area 12 millimeters square (144 square millimeters) would provide sufficient area for the illuminating beam to produce valid reflectance curves. Pigments diluted to 0.1 per cent with lithOpone would provide valid reflectance curves, with 10 milligrams of the mix necessary to provide adequate cov— erage of the window area. Paint specimens diluted to l per cent with lithopone produced reflectance curves of little value for comparison 65 purposes unless the paint Specimens are of a sufficiently dark color. Light colored paint Specimens required a 5 per cent concentration of the specimen-lithopone mix with 10 milligrams of the mix needed to provide adequate cover- age of the window area. The paint Specimen must be capable of being ground to a powder to produce repeatable curves. Linseed oil and polyvinyl acetate were used as vehicles in this study to produce the Specimen smears on glass Slides. Polyvinyl acetate is more advantageous because it dries fast and has a relatively straight reflectance curve. Linseed oil takes a week to dry, has absorption in the Shorter wave— length regions and yellows with age. By grinding the paint chip Specimens, certain surface characteristics due to aging and weathering are destroyed. These characteristics may be examined before grinding. This study has Shown that the reflectance Sphere on the Spectronic 505 has limited value for the comparison of minute paint Specimens even if the paint specimen is diluted with a white pigment to provide greater area of coverage required for the illuminating beam. II. PROPOSED STUDY Carl Zeiss, Inc., has recently developed a reflectance attachment for its Spectrophotometer so that 1 Square millimeter of paint can be examined.4 4"Quick, Watson! The Gamma Spectrometer," The Clini- cal Laboratory, Vol. 31 (1963), p. 101. 66 A means of modifying the reflectance Sphere of the Spectronic 505 to examine minute paint chip Specimens with— out treatment would give this instrument more application in the Forensic Science Laboratory. Condensing the illumi- nating beam onto the Specimen being examined may be one approach to such a modification. BIBLIOGRAPHY BIBLIOGRAPHY A. BOOKS A. §. I. M. Standards 1961. Part No. 8, Designation D307—44. Part No. 8, Designation Dl6-59. Part No. 8, Designation D986—50. . Part No. 8, Designation D97-55. Part No. 9, Designation D791—6lT. Bausch and Lomb Bulletin on Specifications. Catalog Numbers D—2009, 0263. Bausch and Lomb Trichromatic Coefficient Computing Form for Illuminant_g, Catalog No. 33-29-12. Clark, G. L., Editor, The Encyclopedia 9f Spectroscogy. New York: Reinhold Puolishing Corporation, 1960. Committee on Colorimetry, Optical Society of America. The Science 9: Color. New York: Thomas Y. Crowell Co., 1953. Gardner, H. A. and G. G. Sward. Paint, Varnishes, Lacguers, and Colors. Twelfth edition; Bethesda, Maryland: Gardner Laboratories, Inc., 1962. Infrared Spectroscogy. Its Use as an Analytical Tool in the Field 9: Paints and Coatinqs. Chicago Society for Paint Technology, 1960. Judd, D. B. Color in Business, Science and Industry. New York: John Wiley & Sons, Inc., 1952. Kappelmeier, C. P. A., Editor. Chemical Analysis of Resin— Based Coating Material. New York: Interscience Pub— lishers, Inc., 1959. Kirk, P. L. Crime Investigation. New York: Interscience Publishers, Inc., 1960. Mellon, M. G. Colgrimetry fgr Chemists. The G. Frederick Smith Chemical Company, 1945. Morgan, W. D., Editor. The Encyclopedia g; Photography. New York: Graystone Press, 1963. 68 69 O'Hara, C. E. and J. W. Osterburg. Ag Introduction to Criminalistics. New York: The MacMillan Co., 1963. Paint Industry Technical Yearbook and Materials Manual. Philadelphia, Pennsylvania: Heckel PubliShing Company, 1960, Volume 5. Paint Manual. United States Department of Interior, U. S. Government Printing Office. 1961. Payne, H. T. Organic Coating Technology. New York: John Wiley and Sons, Inc., 1961. Volume II. Reference Manual for the Soectronic 505 Spectrophotometer, Catalog No. 33-28-04. Bausch and Lomb, Inc. Rochester, N. Y. Zahn, E. A. Scientific Paint Evaluation. Dayton, Ohio: Research Press, Inc. 1955. B. ARTICLES Atherton, D. and Tough, D. 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Gibbons, D., "Activation Analysis—-An Aid to Forensic Inves— tigation," Forensic Science Society Journal, IV (1963), p. 33. 7O Griffiths, T. R., Latt, K., Symons, M. "Diffuse Reflect— ance Spectrophotometry in the Ultraviolet Using Powder Salts," Analytical Chemistry, XXXI (1959), p. 1338. Quinn, V. P. and Wagner, C. D. "Instrumental Neutron Activation Analysis," Analytical Chemistry, XXXI (1960), p. 317. Hanson, N. W. "Analysis of Paints, Lacquers, and Varnishes," Journal of the Oil and Colour Chemisto' Association, XXXXI (1958), p. 210. Harkins, T. R., J. T. Harris, and O. Shreve. "Identifica- tion of Pigments in Paint Products by Infrared Spectro— SCOpy," Analytical Chemiotry, XXXI (1959), p. 541. Heilman, W. R. "Nondestructive Infrared and X-Ray Diffrac- tion Analysis of Paints and Plastics," Journal of Foreosic Science, V (1960), p. 338. Katzin, L. 1., "Reflection Spectra of Some Solid Cobalt (II) Salts in the Visible Refion," Journal of the American Chemical Society, LXXV (1953). p. 2830. Keller, J. D. "Fundamentals of Spectrophotometry," Bausch and Lomb Booklet No. l, p. 19. Kelly, K. L., K. Gibson and D. Nickerson. "Tristimulus Specification of the Munsell Book of Color from Spectro— photometric Measurements " Journal of the Ootioal Society of America, XXXIII (1943), p. 355. Klug, F., O. Schubert and L. L. Vagnina. "A Microchemical Procedure for Paint Chip Comparisons," Journal of Foronsic Science, IV (1959), p. 91. Kortum, G. "Diffuse Reflectance Spectra of Mercuric Iodide on Different Adsorbents " Transactions of the Faraday Society, XXXXVIII (1962), p. 1624. Kortum, G., and Schreyer, G. "Validity of the Kubelka-Munk function for reflection Spectra with powders," ;. Mateerforsch, CXIV, (1957), p. 1018. Kubelka, P. and T. Munk. "Opacity of Translucent Materials," ;. Tech. Physics, x11 (1931), p. 593. Lermond, C. A., and Rogers, L. B. "Differential Measurements of Reflectance," Analytical Chemistry, XXVII (1955), p. 340. Perkons, A. K., et. al., "Further Development to Forensic Activation Analysis," Proceedings of the Canadian Society of Forensic Science, III (I964), p, 40, 71 "Quick, Watson! The Gamma Spectrometer," The Clinical Lab— oratory, Fisher Scientific, XXXI (1953), p. 98. "Reflectance Attachments Provide Data for Precise Calcula— tion of Tristimulus Color Values," Beckman Application Data Sheet DK-78—MI. Beckman Instruments, Inc. Fullerton, California. Reimann, G., Judd, D. B., and Hiegan, H. J. "SpectrOphoto- metric and Colormietric Determination of the Colors of the TCCA Standard Color Cards," Journal of the Optical Society of America, XXXVI (1946), p. 128. Ruch, R. R., et al., "Neutron Activation Analysis in Scientific Crime Detection--Some Recent DevelOpments," Journal of Forensic Sciences, IX (1963), p. 119. Saltzman, Max. "Color Matching via Pigment Identification," Dyestuffs, XXXXIII (1959). p. 57. Schuster, K. "Radiation from Self—luminous Foggy Atmosphere of a Star," Astrophysics J., XXI (1905), p. 1. Seavell, A. J. "Colorimetry in Paint Industry," Journal of the Oil ano Colour Chemists' Association, XXXX (1957), p. 87. Sendroy, J., and Granville, W. C. "Application of Reflect- ance Spectrophotometry to Quantitative Microanalysis," industrial and Saginaw mm, XIX (1947), p. 500. Stearns, H. I. "Spectrophotometry and the Colorest," American Dyestuff Reporter, XXXIII (1944), p. 18. Tippett, C. F. "The Identification of Make, Model and Year of Manufacture of a Car by an Examination of its Paint Flakes," Medicine, Science and the Law, IV (1964), p. 22. Ulrich, W. F., F. Kelley and D. C. Nelson. "Evaluation of Colorants by Spectrophotometric Methods," Paint Industry Magazine, LXXIV (1959), p. 11. "Use of a Recording Spectrophotometer in the Examination of Evidence," 13.15.11. Law Enforcemsint Bulletin. XV (1946). p. 6. Wendlandt, S., et al. "High Temperature Diffuse Reflectance Spectrosc0py," Analytical Chemistry, XXXV (1963), p. 105. Wendlandt, W. "The Dynamic Reflectance Spectrosc0py," Science, CXXXX (1963), p. 1085. Williams, J. F. "Examination of Paint Chips and Scrapings with the Spectrophotometer," Journal of Criminal Law, Criminology and Police Science, XXXXIV (1954), p. 647. 72 Zeitlin, H., and Niimoto, A. "Comparison of Transmittance and Reflectance Spectra of the 2, 4-Dinitrophenyl- hyrazones of Acetone and 4-Methyl-2pentanone," Aoolyiiool Chemistry, XXXI (1959), p. 1167. C. CORRESPONDENCE Correspondence with Bausch and Lomb, Inc., Rochester 2, New York. 9 anti USE Bid-‘1 {1 ““1 I ‘ _ ‘ 33‘ 5‘ 3? 4, ‘1 ”7111111119111”: ((1111111111“