(Received 13 April 1998; accepted 16 July 1998)
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As part of a study of the chemical compositions of U.S. automobile original topcoats (1974 to 1989) using infrared spectroscopy, a number of organic pigments used in these finishes have been identified. The topcoats examined were single-layer finishes (monocoats) from the Reference Collection of Automotive Paints, and pigments from the benzimidazolone and quinacridone families were previously identified. The in situ identification of two other organic pigments used in these finishes, DPP Red BO and Thioindigo Bordeaux, is described here. DPP Red BO is a relatively new pigment which was first marketed in 1987, and it was only identified in two red nonmetallic enamels produced in 1989, the last year covered in this study. It is now quite common in automotive paints and its presence in an unknown original finish indicates that a fairly recent vehicle (most likely from the 1990s) was the source. In contrast, Thioindigo Bordeaux, which was identified in a few red and brown nonmetallic and brown metallic enamels, was more common in the 1950s and 1960s but was largely replaced by Quinacridone Violet in the 1970s. It is no longer used much in automotive paint. Spectra of several DPP automotive paint pigments introduced after 1989 are also presented and discussed.
Forensic scientist, Washington State Crime Laboratory, Washington State Patrol, Seattle, WA
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