1. Forensic Examination of PaintPg

2. Paint is…
Pigments (organic and inorganic) and additives suspended in a polymeric binder solution
One of the most prevalent types of physical evidence
Most often recovered in burglary and hit-and-run cases

3. Paint comparisons Need 2 paint samples for comparison OR
Can examine uniqueness of one paint sample
Comparison analysis can
Link a person or vehicle to a crime scene OR
Identify the color, make, and model of the vehicle that left the paint sample at the scene

4. Automobile paint Each manufacturer applies a specific variety of coats
For steel auto finishes:
4 coats
Electrocoat primer
Primer surfacer
Basecoat
Clearcoat

5. Electrocoat primer Black to gray in color
Electroplated to the steel surface
Uniform in appearance and thickness
Provides corrosion (rust) resistance
Made of epoxy-based resins

6. Primer surfacer Originally used for corrosion control
Now used for smooth out and hide any seams or imperfections
Highly pigmented – different colors (gray to red) used to minimize the contrast between the primer and the basecoat
Made of epoxy-modified polyesters

7. Basecoat (or colorcoat)
Provides the color for aesthetic appeal
Integrity based on resistance to the elements (UV radiation, acid rain, weather)
Contains acrylic-based polymer binder
Pigments dictated by toxicity – no lead, chrome, or other heavy metals
Organic-based pigments used now – mica, pearl luster, aluminum flakes

8. Clearcoat Unpigmented Provides glossy appearance, improves durability
Mostly acrylic-based but some polyurethane

9. Comparing paints Stereoscopic microscope (stereoscope)
Color is most distinctive characteristic
Also compare surface texture, shape, and color layer sequence

10. Color layer sequence Compare
Number of layers
Sequence of colors
Matching samples is dependent on the uniqueness of each layer (color, thickness, etc.)
No definite number of layers to guarantee a match

11. Chemical composition Of pigments or binders
Pyrolysis gas chromotography
Paint samples are decomposed by heat into gases and then identified through gas chromatography
The “pyrogram” or chromatogram gives the unique chemical composition of the pigment or binder
Can also use
infrared spectrophotometry (unique spectrum),
emission spectroscopy,
X-ray diffraction or spectroscopy

13. If samples are compared by layer structure, solvent tests, pyrolysis gas chromatography, and x-ray spectroscopy…
The chance of an incorrect match is ,000 to 1

14. Paint databases
Law Enforcement Standards Laboratory collection distributed through Collaborative Testing Services in McLean, VA
Royal Canadian Mounted Police Forensic Laboratory’s PDQ (Paint Data Query)