Over the past four decades, substantial efforts have been made to develop and validate databases, technologies, and consensus-based standards that describe the importance of glass and paint as physical evidence. However, applying broader interpretation approaches beyond the source level still requires local data about how common trace materials are among the general public compared to those involved in an alleged criminal incident. This project fills this gap by examining essential factors that have never been evaluated together in a single, systematic study. It provides data on the prevalence of glass and paint residues from four different cities across two regions of the United States, including both small and metropolitan areas with diverse socioeconomic and demographic backgrounds. The study also assesses how often these traces appear across different seasons. It considers factors that may affect the retention of glass and paint on clothing, such as transportation modes and the types of clothing and footwear worn. Finally, a detailed analysis of the features of the recovered traces using appropriate techniques allows for the assessment of the significance of glass and paint presence based on their main source products.
A total of 2,391 garments and pairs of footwear were sampled from 510 volunteers across six locations: the upper and lower surfaces, embedded areas on the top and bottom clothing, as well as the footwear surfaces and embedded areas such as soles. The most significant findings of this study are: 1) Paint traces were more common in the general population than glass (paint found in 24% of the overall population and 0.6% of the items, compared to glass in 2.9% of the population and 0.6% of the items). 2) Glass was mainly recovered from the surfaces and soles of footwear. In comparison, paint was primarily found on the upper and lower surfaces of garments. 4) Most individuals and items examined contained a single glass or paint fragment, with a few exceptions that contained multiple fragments. No more than two fragments were observed from a single group. 5) Glass and paint traces were predominantly small (most glass < 1 mm, most paint < 0.5 mm). 6) The parallel occurrence of glass and paint in a single individual was very rare (0.4%). Even more uncommon to find both traces in a single item (0%). 7) Most of the glass recovered from background populations was identified as container or sheet soda-lime-silicate glass, with a few specialty formulations like phone screen protectors, high-iron glass fragments, and zinc-phosphate glass. This suggests that forensic practitioners might begin to encounter modern glass more frequently in casework. 8) Most of the paint recovered from the general population was single-layered architectural or automotive paint with various binders and pigment compositions, while some residues suggest the presence of potential nail polish formulations. 9) A higher occurrence of glass and paint was observed in winter compared to summer, indicating that clothing and primary transportation methods during these seasons influence the background of the traces. 10) The demographics, socioeconomic conditions, and urban design of the cities affect the occurrence rates of glass and paint. The factor showing the most significant difference across the four cities was the mode of transportation.
This study offers essential data and resources to develop a knowledge base necessary for maximizing trace evidence applications in the United States beyond source attributions, including activity-related reconstruction leads and evidence interpretation in criminal investigations.
(Author abstract provided.)
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