Analyzing Paint
with
Infrared Spectroscopy
THE ANALYTE: Paint (from a car, or on a weapon or someone's clothing...)
THE IDENTITY TEST: Paint has been recovered from a crime scene. Investigators must record the evidence and keep track of it. Since there is a limited amount of paint, the first tests to be done should be nondestructive. Colors, layers, texture, and other physical properties are recorded, using a microscope as well as the naked eye.
Finally, the individual layers of paint are analyzed by infrared spectroscopy. The results can be compared to IR results of known paint.
THE IDENTITY AND THE CRIME:
SCENARIO #1: There has been a hit-and-run accident. The victim has paint smears on their clothing. A witness remembers part of the license plate. There are several possibilities.
After narrowing the cars down to those with a overcoat of paint the same color as the smear, the sample is analyzed with IR. Using a computer database of car paint processes, the paint is identified with a specific make, model, and year of vehicle.
The possible cars are narrowed down to one. The investigators use a combination of the IR results and other evidence to prosecute the owner of the vehicle.
SCENARIO #2: A robber has broken into a home using a blunt object. After obtaining a warrant, investigators find that a suspect is in possession of a crowbar that has some crushed paint chips on the end.
Using infrared spectroscopy, a forensic chemist matches the paint on the crowbar to paint on the door of the house that was burglarized. The suspect is convicted and sent to trial.
Read the FBI's Forensic Paint Analysis and Comparison Guidelines.
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