Paints forensic analysis

There is now available laser ablation ICP-MS which allows solid samples to be analysed directly. It is an important techniqne for nse in the forensic analysis of vehicle paint samples at the scene of hit-and-rnn crimes . 

In forensic science, FTIR microscopy has been used to examine paint chips from automobile accidents. An example of a paint chip spectmm is shown in Fig. 4.29. Hit-and-run drivers frequently leave traces of paint on cars with which they collide. Identification of the paint can help to identify the car. Other uses of an IR microscope in forensic analysis include the examination of hbers, dmgs, and traces of explosives. 

The Py-GC examination of paint, in the context of an overall forensic analysis of this type of evidence, has been described. ... 

Finally, in many cases the pyrolysis product distribution is so complex that it is not possible to separate and identify all of the components. In such cases a chemometric method, simply treating the pyrogram as a pattern, can be used to compare one sample with another. This approach has foimd many applications in forensic analysis, for example, of paints and in analysis of authenticity of art works (54). It has even been used to type bacteria (55-57). These applications often take advantage of the fact that the high sensitivity of the analytical method allows minute samples to be analyzed they depend upon a database of pyrograms obtained under well-controlled conditions and analysis involves a statistical pattern-matching approach. 

Another vibrational technique, Raman spectroscopy is gamering attention for the forensic analysis of drugs and pharmaceuticals, paints, fibers, and inks. Raman techniques differ from traditional vibration IR in that scattered radiation, rather than absorbed radiation, is studied. Furthermore, Raman interactions are dependent, not on the existence of polar bonds, but instead on the existence of polarizable bonds as shown in Figure 5.36. 

The Munsell color system is conceptually similar to the QELAB system, but with some significant differences. The Munsell system was conceived by the American painter Albert H. MunseU in 1905 with subsequent revisions and variations. The three variables used to describe colors in the system are hue, brightness (similar to lightness in QELAB), and saturation (similar to chroma also called value). As shown in Figure 11.14, the color space is cylindrical. The hue is divided into 100 equal spaces around the circle that forms the cross section of the cylinder, while the y direction is the brightness, scaled from 0 to 18. The x-axis is the saturation, scaled from 10 to 18. Munsell charts and collections are used in the forensic analysis of paints and soils. Because books and samples of color are used for color comparison, the Munsell color space is sometimes referred to as a catalog system. An example application is in soil analysis in which soil particles can be seived, sorted, and grouped by their Munsell color. 

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