Summary Assessment

As is the case with fiber evidence, analysis of paints and coatings is based on a solid foundation of chemistry to enable class identification. Visual and microscopic examinations are typically the first step in a forensic examination of paints and coatings because of the ability to discriminate paints/coatings based on properties determined with these examinations. Several studies have been conducted that included hundreds of random automotive paint samples.110 These studies have concluded that more than 97 percent of the samples could be differentiated based on microscopic examinations coupled with solubility and microchemical testing. Another study111 determined that more than 99 percent of 2,000 architectural paint samples could be similarly differentiated. However, the community has not defined precise criteria for determining whether two samples come from a common source class.

ANALYSIS OF EXPLOSIVES EVIDENCE AND FIRE DEBRIS

Explosives evidence encompasses a wide range of materials from unburned, unconsumed powders, liquids, and slurries, to fragments of an explosive device, to objects in the immediate vicinity of an explosion thought to contain residue from the explosive. A typical analytical approach would be to identify the components and construction of an explosive device and conduct an analysis of any unconsumed explosives and residues. In addition to the analysis and identification of low and high explosives, chemical reaction bottle bombs are also analyzed. The scene of an explosion can require special investigative attention. What may appear to be a small piece of scrap metal could in fact be an important piece of the device that caused the explosion. The very nature of an explosion has a direct impact on the quality of evidence recovered. Pristine devices or device fragments, or appreciable amounts of unconsumed explosive material, should not be expected.

Analyses

Generally speaking, laboratories will not accept devices until they have been rendered safe. Examiners involved with the analysis of explosives evidence in the laboratory typically have an extensive scientific background, because the methods used entail a large amount of chemistry and instru-

110

S.G. Ryland and R.J. Kopec. 1979. The evidential value of automobile paint chips. Journal of Forensic Sciences 24(1):140-147; J.A. Gothard. 1976. Evaluation of automobile paint flakes as evidence. Journal of Forensic Sciences 21(3):636-641.

111

C.F. Tippet. 1968. The evidential value of the comparison of paint flakes from sources other than vehicles. Journal of the Forensic Sciences Society 8(2-3):61-65.



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