(Received 5 February 1999; accepted 8 March 1999)
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Two yellow organic pigments, Benzimidazolone Yellow 3G and Benzimidazolone Yellow 4G, were identified in some U.S. automobile original (OEM) topcoats (1974–1989) in previous work in this study. The topcoats consisted of single layer finishes (monocoats) from the Reference Collection of Automotive Paints, and the pigments were identified in situ using infrared spectroscopy. The identification, analysis, and occurrence of other yellow organic pigments used in these finishes, including Isoindolinone Yellow 3R, Isoindoline Yellow, and Anthrapyrimidine Yellow, are described here. Based on a spectral survey of Reference Collection yellow, orange, brown and green nonmetallic monocoats, absorptions of Isoindolinone Yellow 3R were observed in the spectra of approximately three dozen yellow monocoats and one dozen orange ones. Isoindoline Yellow was identified in a single orange nonmetallic enamel. This pigment is now more common since it was one of several replacements for Chrome Yellow—a popular lead-containing pigment which is no longer used in U.S. automobile OEM finishes—and it was identified in several recent yellow nonmetallic basecoat/clearcoat finishes. Weak absorptions of Anthrapyrimidine Yellow were identified in the spectrum of a single yellow nonmetallic enamel. Spectra of several other yellow organic automotive paint pigments are also presented and discussed.
Forensic scientist, Washington State Crime Laboratory, Washington State Patrol, Seattle, WA
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