Examination of Paint

1. Examination of Paint • Examine two paint samples to determine same origin • Generally used in burglaries, hit-and-run accidents or vehicle accidents

2. Composition of Paint • Paint is composed of a binder, pigments and additives dissolved in a solvent • Paint is spread onto a surface and dries in a hard film • As it dries, the solvent evaporates leaving behind the binder and pigments suspended in it

3. Automotive Paint Layers • Electrocoat primer: applied to steel body to prevent corrosion, generally gray or black • Primer Surfacer: Completely smoothes out surface. Highly pigmented to minimize difference in color between basecoat and primer

4. Automotive Paint Layers, cont’d • Basecoat: Provides the color and finish of the car. Must be able to resist UV rays, weather and acid rain. • Clearcoat: Un-pigmented layer used to improve gloss and durability of the paint

5. Examination of Paint • Color determination is used to identify paint • Two paint samples would be examined under stereoscopic microscope for color, surface texture and color layer sequence • An increase in the complexity of the layer structure gives a sample greater forensic value

6. Examination of Paint, cont’d • Use pyrolysis gas chromatography to determine paint formulation • IR Spectrophotometry is used to determine composition of paint • Analyze the inorganic pigments in paint using neutron activation analysis, X-ray diffraction and X-ray spectroscopy. • Compare paint make-up to color charts maintained by car manufacturers to determine make and year of car

7. Collection and Preservation of Paint Evidence • Pick up with forceps or scooped up with paper • Use druggist folds or glass vials to contain paint • Collect standard/reference sample when available using clean scalpel or Exacto Knife