Forensic science - paint analysis

Forensic Paint Analysis

Paint analysis , in the context of forensic science , is the process of examining paint samples in an attempt to discover their unique physical and chemical properties . Usually this is done on known and questioned samples to check for any differences between them , and thus to determine if they are from the same source . One of the areas in which forensic paint analysis is particularly useful is in motor vehicle identification , when paint is collected from an accident or crime scene for example . However , since paint samples from the same

source can also have differences in its physical or even chemical characteristics forensic paint analysis also involves the assessment of the significance of any differences in tested samples

The physical match

This is the most straightforward and conclusive examination that can be done . It usually involves the comparison of the edges and surface markings on the paint samples , and surface markings on the underside of the samples to the original surface . Physical matches must be documented by taking images and notes

The layers of paint are visually identified by viewing sample edges at 5-100 times magnification , to make definitive layer identification sample preparation techniques are necessary . Subtle differences in the physical characteristics between paint samples should be tested for by viewing samples side by side on a microscope

Solvent /Microchemical Tests

When paint samples have very similar visual and physical characteristics , they can be put through solvent or microchemical tests to check for chemical differences between them

The tests involve dissolving paint binders and the reactions of pigments and binders with dehydrating , oxidizing , and reducing agents . These tests are destructive and thus should only be used if the amount of questioned samples is sufficient . Tests should be done , and changes recorded , on known and questioned samples simultaneously . The changes which can include softening , warping , layer dissolution , flocculation and color changes , can be difficult to quantifiy , thus this should be considered to be only preliminary testing

Polarized Light Microscopy (PLM

PLM can be used for examining the layer structure and the particles such as pigments and extenders , in a paint sample , by observing their optical properties

Infrared Spectroscopy

Information about binders , pigments , and additives , can be obtained through this method . A beam-focusing device is usually necessary . The infrared light beam is split into two separate beams and passes through the sample (which has been dissolved , and the other through the substance in which the sample has been dissolved . The beams are then reflected and read , and the differences in spectral absorption patterns are obtained

Pyrolysis Gas Chromatography (PGC

Chromatography is a family of analytical chemistry techniques for the separation of mixtures . In gas chromatography a substance is processed in a chromatograph , which separates the chemicals into its component parts because of the different migration rates of the components of the substance through the chromatographic medium because of different affinity values

Pyrolysis gas chromatography involves heating samples for several seconds at very high temperatures (such as 600 degrees Celsius ) inside...