Forensic Chemistry: Paint Multilayer Analysis with PDQ, SEM-EDX and FTIR

Paint evidence is one of the most information-dense trace materials recovered at crime scenes, particularly in hit-and-run road incidents. This medium-difficulty UGC-NET Forensic Science Paper II Unit VII drill covers the complete analytical workflow from paint chip collection through instrumental characterisation and database comparison. The set addresses paint layer architecture (binder or resin, pigment, solvent, and additives such as driers and surfactants), the automotive multilayer system (electrocoat or e-coat primer, primer-surfacer, colour basecoat, and clearcoat), the chemical distinctions between architectural and automotive paint, and the chemistry of lacquers based on cellulose nitrate versus polyurethane and alkyd varnishes. Instrumental methods covered include SEM-EDX for elemental mapping of inorganic pigments (differentiating TiO2 rutile from anatase, identifying iron oxide red Fe2O3, and detecting chromium oxide Cr2O3 in primers), FTIR spectroscopy for organic binder identification (alkyd, epoxy, acrylic, and polyurethane resins each carry diagnostic carbonyl and backbone absorption bands), micro-Raman for non-destructive pigment identification at the nanogram scale, and pyrolysis-GC-MS for resin polymer fingerprinting. The PDQ (Paint Data Query) database maintained jointly by the RCMP, FBI, and EUROPOL is addressed as the global hit-and-run paint reference resource, including the mechanism of Indian CFSL participation through the DFSS (Database for Forensic Science Standards) linkage.

The set is aimed at UGC-NET Forensic Science Paper II aspirants targeting Unit VII (Trace Evidence), NFSU MSc Forensic Chemistry students, FACT aptitude candidates, and CFSL Chandigarh paint and glass section trainees. Questions are calibrated to the SWGMAT paint subgroup guidelines and Caddy's Forensic Examination of Glass and Paint, supplemented by Saferstein Criminalistics 12th edition and Sharma B.R. for Indian context.

Topics covered:

• Paint layer components: binder, pigment, solvent, drier and surfactant additives
• Automotive multilayer: e-coat, primer-surfacer, colour basecoat, clearcoat
• Architectural vs automotive paint: binder type, layer count, application method
• Lacquer and varnish chemistry: cellulose nitrate vs polyurethane binder
• PDQ database: RCMP/FBI/EUROPOL maintenance, CFSL India via DFSS
• SEM-EDX: TiO2 rutile vs anatase, Fe2O3, Cr2O3 inorganic pigment mapping
• FTIR: alkyd, epoxy, acrylic, polyurethane binder identification
• Hit-and-run paint chip: cross-section examination, layer sequence transfer

Work through each question before reading the explanation, and revisit wrong answers against the Caddy, Saferstein, SWGMAT, and PDQ references cited. Allow 30 minutes.