July 1999 - Volume 1 - Number 2

Forensic Paint Analysis and Comparison Guidelines

9.0. Other Techniques

9.1. Fluorescence Microscopy
9.1.1. Fluorescence microscopy of thin or bulk cross sections, as an aid in differentiating samples or various layers within intact paint fragments, is discussed by Stoecklein and Tuente (10). When using an excitation wavelength of 365 nanometers, the technique may be sensitive to differences in organic pigments, additives, and film-forming components. Allen (53) reports it to be most useful with light-colored architectural coatings.

9.2. Low-Temperature Ashing
9.2.1. The low-temperature asher is a device in which an oxygen plasma is used to remove organic materials from a complex matrix. Materials that produce volatile oxides (principally organic components) are removed from the matrix with minimal elevation of the sample temperature in contrast to pyrolysis systems. Ashing usually continues until all such volatile oxides are removed.

9.2.2. Inorganic pigments, extenders, and some additives in the different layers of the ashed paint film will remain after the organic material is volatilized. The relative size and morphology of the different particles, noted during previous tests, serve to help identify and separate these residue components for additional analysis. A brief description of the technique is provided by McCrone and Delly (54) and Brown (55).

9.2.3. Ashing residues can be analyzed by a variety of methods, including PLM, SEM-EDS, analytical electron microscopy (AEM), or XRD techniques.

9.3. Solvent Extraction
9.3.1. Solvent extraction can be used to separate some of the organic components from paint films, depending on the paint system or systems in question. The objective of the procedure is to recover a solute that can be examined by IR, GC, or GC-MS techniques. It is especially useful for coatings where the volume of pigments or extenders is very high. The identification of the binders by FTIR is often only possible after separation of the pigments and extenders.

9.3.2. When using solvent extraction, separation of paint layers is very important. If this is impossible, it is important that identical conditions (e.g., time, and temperature) be applied to both the known and questioned samples.

9.4. Analytical Electron Microscopy
9.4.1. Analytical electron microscopy (AEM) is the term applied to the use of transmission electron microscopy (TEM) in conjunction with both selected area electron diffraction and EDS. The combination of techniques can provide more definitive identification of some pigment grains that cannot be identified conclusively by PLM because of their extremely small size or opacity.

9.4.2. AEM requires that the sample be sufficiently thin to permit transmission of the analytical electron beam. It is thus applied only to dispersions of extracted inorganic particulates, such as those recovered from low-temperature ashing, dissolved paint layers, or ultramicrotomed sections of a paint film (56).

9.5. Cathodoluminescence
9.5.1. Cathodoluminescence (CL) is the emission of radiation from the sample in the visible light region and neighboring wavelengths following excitation by electrons where these, originating from a cathode and accelerated in an electric field, strike upon an insulator or semiconductor (e.g., inorganic pigments or fillers). This phenomenon can be observed through the use of specially equipped optical or scanning electron microscopes.

9.5.2. Cathodoluminescence can be performed on embedded sections as an aid in differentiating samples or various layers within intact paint fragments. The technique has been found to be most useful for characterizing and comparing multilayered white or beige architectural and marine paint fragments (57).

10.0. References

(1) Scientific Working Group for Materials Analysis. Trace Evidence Quality Assurance Guidelines. Federal Bureau of Investigation, Washington, DC, 1999.

(2) Scientific Working Group for Materials Analysis. Trace Evidence Recovery Guidelines. Federal Bureau of Investigation, Washington, DC, 1998.

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(8) Laing, D. K., Locke, J., Richard, R. A., and Wilkerson, J. M. The examination of paint films and fibers as thin-sections, Microscope (1987) 35:233-248.

(9) Allen, T. J. Modification of sample mounting procedures and microtome equipment for paint sectioning, Forensic Science International (1991) 5:93-100.

(10) Stoecklein, W. and Tuente, J. Using the light microscope for analytical aids for solving cases involving hit-and-run offenses, Zeiss Information With Jena Review (1994) 3:19-22, 669-678.

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(20) Allen, T. J. Paint sample presentation for Fourier transform infrared microscopy, Vibrational Spectroscopy (1992) 3:217-37.

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(22) Rodgers, P. G., Cameron, R., Cartwright, N. S., Clark, W. H., Deak, J. S., and Norman, E. W. W. The classification of automotive paint by diamond window infrared spectrophotometry: Automotive topcoats and undercoats, Canadian Society of Forensic Science Journal (1976) 9:49-68.

(23) Rodgers, P. G., Cameron, R., Cartwright, N. S., Clark, W. H., Deak, J. S., and Norman, E. W. W. The classification of automotive paint by diamond window infrared spectrophotometry: Case histories, Canadian Society of Forensic Science Journal (1976) 9:103-111.

(24) Norman, E. W. W., Cameron, R., Cartwright, L. J., Cartwright, N. S., Clark, W. H., and MacDougall, D. A. The classification of automotive paint primers using infrared spectroscopy: A collaborative study, Canadian Society of Forensic Science Journal (1983) 16:163-173.

(25) Suzuki, E. M. Infrared spectra of U.S. automobile original topcoats (1974-1989): Differentiation and identification based on acrylonitrile and ferrocyanide C=N stretching absorptions, Journal of Forensic Sciences (1996) 41:376-392.

(26) Suzuki, E. M. Infrared spectra of U.S. automobile original topcoats (1974-1989): Identification of some topcoat inorganic pigments using an extended range (4000-220 cm^-1) Fourier transform spectrometer, Journal of Forensic Sciences (1996) 41:393-406.

(27) Suzuki, E. M. and Marshall, W. P. Infrared spectra of U.S. automobile original topcoats (1974-1989): In situ identification of some organic pigments used in yellow, orange, red and brown nonmetallic and brown metallic finishes - benzimidazolones, Journal of Forensic Sciences (1997) 42:619-648.

(28) Infrared Spectroscopy Atlas Working Committee, An Infrared Spectroscopy Atlas for the Coatings Industry, 4th ed. (Vols. 1 and 2). Federation of Societies for Coatings Technology, Blue Bell, Pennsylvania, 1991.

(29) Kuptsov, A. H. Applications of Fourier transform Raman spectroscopy in forensic science, Journal of Forensic Sciences (1994) 39:305-318.

(30) Claybourn, M., Agbenyega, J. K., Hendra, P. J., and Ellis, G. Fourier transform Raman spectroscopy in the study of paints, Advances in Chemistry Series (1993) 236:443-482.

(31) Burke, P., Curry, C. J., Davies, L. M., and Cousins, D. R. A comparison of pyrolysis mass spectrometry, pyrolysis gas chromatography, and infrared spectroscopy for the analysis of paint resins, Forensic Science International (1985) 28:201-219.

(32) Fukuda, K. The pyrolysis gas chromatographic examination of Japanese car paint flakes, Forensic Science International (1985) 29:227-236.

(33) Cassista, A. R. and Sandercock, P. M. L. Comparison and identification of automotive topcoats: Microchemical spot tests, microspectrophotometry, pyrolysis gas chromatography, and diamond anvil cell FTIR, Canadian Society of Forensic Sciences Journal (1994) 27:209-223.

(34) Blackledge, R. D. Application of pyrolysis gas chromatography in forensic science, Forensic Science Review (1992) 4:2-15.

(35) Challinor, J. M. Forensic application of pyrolysis capillary gas chromatography, Forensic Science International (1983) 1:269-285.

(36) Saferstein, R. and Manura, J. J. Dual column pyrolysis gas chromatography, Crime Laboratory Digest (1988) 15:39-43.

(37) Irwin, W. J. Analytical pyrolysis: An overview, Journal of Analytical and Applied Pyrolysis (1979) 1:3-25.

(38) Wampler, T. P. Analytical pyrolysis: An overview and instrumentation and analysis. In: Applied Pyrolysis Handbook, Wampler, T. P. (ed.). Marcel Dekker, New York, 1995, pp. 1-54.

(39) Freed, D. J. and Liebman, S. A. Basic analytical pyrolysis instrumentation. In: Pyrolysis and GC in Polymer Analysis, Liebman, S. A. and Levy, E. J. (eds.). Marcel Dekker, New York, 1985, pp. 15-51.

(40) Liebman, S. A. and Wampler, T. P. Analysis of polymeric materials: Advanced pyrolysis instrumentation systems. In: Pyrolysis and GC in Polymer Analysis, Liebman, S. A. and Levy, E. J. (eds.). Marcel Dekker, New York, 1985, pp. 15-51.

(41) McMinn, D. G., Carlson, T. L., and Munson, T. O. Pyrolysis capillary gas chromatography-mass spectrometry for analysis of automotive paints, Journal of Forensic Sciences (1985) 30:1064-1073.

(42) Challinor, J. M. Examination of forensic evidence. In: Applied Pyrolysis Handbook, Wampler, T. P. (ed.). Marcel Dekker, New York, 1995, pp. 207-217.

(43) Challinor, J. M. Structure determination of alkyd resins by simultaneous pyrolysis methylation, Journal of Analytical and Applied Pyrolysis (1991) 18:233-244.

(44) Challinor, J. M. The scope of pyrolysis methylation reactions, Journal of Analytical Pyrolysis (1991) 20:15-24.

(45) Challinor, J. M. Pyrolysis derivitization using tetraalkylammonium hydroxide, Journal of Analytical Pyrolysis (1993) 16:323.

(46) Cousins, D. R. The use of microspectrophotometry in the examination of paints, Forensic Science Review (1989) 1:141-161.

(47) Derrick, M. R. Infrared microspectroscopy in the analysis of cultural artifacts. In: Practical Guide to Infrared Microspectroscopy, Humecki, H. J. (ed.). Marcel Dekker, New York, 1995, pp. 287-322.

(48) Goldstein, J. I., Newbury, D. E., Echlin, P., Joy, D. C., Romig, A. D., Lyman, C. E., Fiori, C., and Lifshin, E. Scanning Electron Microscopy and X-Ray Microanalysis, 2nd ed. Plenum Press, New York, 1992, pp. 79-90, 334-336.

(49) Gardiner, L. R. The Homogeneity of Modern Household Paints Using Scanning Electron Microscopy: Energy Dispersive X-Ray Analysis (SEM-EDXA), HOCRE Report 408, 1981, pp. 1-6.

(50) Fischer, R. and Hellmiss, G. Principles and forensic applications of x-ray diffraction and x-ray fluorescence. In: Advances in Forensic Science (Vol. 2). Medical, Chicago, 1989, pp. 129-158.

(51) Howden, C. R., Dudley, R. J., and Smalldon, K. W. The non-destructive analysis of single layered household paints using energy dispersive x-ray fluorescence spectrometry, Journal of the Forensic Science Society (1977) 17: 161-167.

(52) Snider, A. M. X-Ray Techniques for Coatings Analysis, Analysis of Paints and Related Materials: Current Techniques for Solving Coatings Problems, Golton, W. C. (ed.). ASTM STP, Philadelphia, 1992, pp. 82-95.

(53) Allen, T. J. Effects of Environmental Factors on the Fluorescence of White Alkyd Paint, CRSE Report 758, 1994.

(54) McCrone, W. C. and Delly, J. G. The Particle Atlas (Vol. 1). Ann Arbor Science, Ann Arbor, Michigan, 1976, pp. 221-222.

(55) Brown, R. Light and electron microscopy of inorganic paint constituents. In: Proceedings of Scanning ‘93, Scanning, 15, Supp. III, 1993, pp. III-35.

(56) Goebel, R. and Stoecklein, W. The use of electron microscopic methods for the characterization of paints in forensic science, Scanning Microscopy (1987) 1:1007-1015.

(57) Stoecklein, W. Application of cathodoluminescence in paint analysis, Scanning Microscopy (1992) 6:669-678.

11.0. Endnotes

¹ Annual Book of Standards, Vol. 06.01.

² Annual Book of ASTM Standards, Vol. 14.02.

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