1. 8.4 Notes
Examination of Paint

2. Objectives
List the most useful examinations for performing a forensic comparison of paint
Describe proper collection and preservation of forensics paint evidence

3. Paint
One of the most prevalent types of physical evidence received by a crime laboratory.
from a hit and run
from a tool during a burglary
Paint is composed of a binder and pigments dissolved or dispersed in a solvent

4. Vocabulary Pigment – color and opacity
Binder – support medium for pigments and additives (polymer)
Solvent – evaporates after application leaving the hard polymeric binder and pigments

5. Automobile finishes The most common types of paint examined
Manufacturers apply a variety of coating to the body
Adds diversity to automobile paint

6. Automotive finishing for steel
Electrocoat primer
first layer consisting of epoxy-based resins
provides resistance from corrosion
usually black to gray
Primer surfacer
applied before base coat
completely smooth out and hides seems and imperfections
highly pigmented

7. Basecoat Clearcoat layer provides color and aesthetics of the finish
usually acrylic based and organic based pigments
some have aluminum flakes and metal oxide
must be able to resist UV radiation, acid rain, and weather conditions
Clearcoat
unpigmented clearcoat used for durability
most are acrylic based and some polyurethane
appearance = glossy finish

8. Stereoscopic microscope
Used for comparing color, surface texture, and color layer sequence
Most specimens do not have a layer structure that allows the criminalist to individualize a chip to a single source
Chemical composition does provide points of comparison between specimens
must include a chemical analysis of either pigments or binder composition

9. Pyrolysis gas chromatography
Useful technique for distinguishing paint formulations
Paint chips or polymer chains are decomposed by heat into gas products then sent through a gas chromatograph
Different polymers show a distinct pattern
details the chemical makeup of a binder or a paint

10. Infrared spectrophotometry
Analytical technique used for binder composition
Inorganic pigments of paints can be identified by
X-ray diffraction
X-ray spectroscopy
Emission spectroscopy
Neutron activation analysis

11. Collection and preservation
Picked up with tweezers or scooped up with paper
Use druggist fold or Glass/plastic vials
Collect whole garments or objects in which paint chip is embedded
Standard/reference samples needed of all paint layers