ALL THE COLORS OF THE RAINBOW - FORENSIC PAINT ANALYSIS - Page: 2

Paint is fun. It's colorful, which makes it a lot more interesting to look at than hairs and often fibers. It can be flat or fancied up with shiny metallic flake. It's surprisingly malleable, able to be flattened and smeared. Unfortunately, paint is also a Pandora's box of information-infinitely complicated and esoteric, impossible to fully understand. Paint is usually encountered in cases involving automobiles, although everything said here applies to wall paint, house paint and nail polish, as well. Hit-skip accidents or road-rage incidents can leave chips or smears of color behind, marking their passage.

In the old days (read: "Dragnet") paint was simple. All GM cars used lacquer, and all Fords used enamels, or something like that. Cut and dried. In our more modern age, paint exists in a spectrum of colors and compositions. Formulas are jealously guarded and change every year as manufacturers experiment and shop around for good deals.

The standard equipment for paint analysis is a Fourier Transform Infrared Spectrometer. This machine sends a laser beam of light through a sample of paint which has been flattened to the point of transparency (or through a thicker sample using reflectance, or an ATR crystal-it really gets quite complicated). The sample might be one or two millimeters square-use a stereomicroscope unless you want to go blind. The point is, the FTIR produces a spectrum, which is a measurement of how much light is absorbed by the paint at different frequencies. It looks something like an EKG. The peaks and valleys on this spectrum tell the scientist what functional groups are present in the compound, say an -OH group, or a carbon-carbon double bond, or titanium dioxide.

The computer attached to the FTIR can then compare the spectrum produced by your paint to a library of spectra of other, known, samples. It will give you a list of spectra which most closely match yours-something like a computerized fingerprint system. Just like a fingerprint system, however, the computer is just a tool. The scientist must study the spectra and decide if they are similar.

Paint is applied to a car in layers. Starting at the metal, the first coat is called an electron coat, or e-coat. This is a very thin layer of dark gray. Then there is one or two coats of primer, usually a grainy gray or red-brown color. Then there is the color coat, the color you actually see when you look at the car. In most modern cars, there is a clearcoat over the color coat, which is, literally, clear. (This will turn white when you flatten it for the FTIR.) If the car has been repaired or repainted, there may be yet another layer of color and another layer of clearcoat. The more layers your unknown chip has in common with your known sample (say, from the suspect's car), the more compelling the evidence.

The FBI and the Canadian Royal Mounted Police have collaborated on an ambitious project called PDQ-Paint Data Query. They have collected spectra on hundreds of thousands of samples of automotive paint, noting the VIN#, year, make and models. The idea is to be able to compare an unknown paint chip with their library and voila, a make and model of car to look for. This does work, and well, but it is a huge undertaking. Crime lab personnel must first be trained in the PDQ computer software. Then they must submit 60 samples of automotive paint each year to the FBI/RCMP in order to receive the updated spectra libraries. Then they must consider the enormous amount of different automobiles in North America without getting discouraged.

Note for accuracy: PDQ does not actually search using the spectra of a sample. The scientist must use the spectra to determine the components of the paint layers, and put that information in a text page. The actual computer search uses the text messages, not the picture of the spectra. Also, the bewildering assortment of colors available these days-poppy, mauve, teal-are reduced to six or seven terms: simply red, green, blue, gold, etc.

FTIR work is more fun than most lab work, so it wouldn't be odd to portray your minor character FTIR technician as a cheerful fellow-except on those days when the paint chip wants to stick to your roller, your tweezers, your fingers, everything except the salt window. Although he might not be so cheery when he encounters the new automotive paints that make a car appear yellow from one direction, and blue from another. Coming soon to a dealership near you.