Spectroscopy allows forensics researchers to tell cosmetics apart
WASHINGTON — Discerning one lipstick from the next can be tough for consumers but it’s even harder for scientists. Now forensics researchers have found a quick method to tell apart individual lipsticks, no matter the color or brand. The approach could help investigators analyze evidence in cases in which a smear of lipstick on glass, paper or a piece of clothing becomes important.
Experts typically examine a lipstick’s dyes or its chemical or elemental composition. To distinguish closely related cosmetics, those approaches usually need to be combined, said Paige Gardner of Virginia Commonwealth University in Richmond. She decided to tackle 80 lipsticks with Raman spectroscopy, which zaps a sample with laser light, making some of the molecules vibrate. These tickled molecules emit light of a frequency different from what came in, and researchers can read that shift in frequency like a chemical bar code.
The approach allowed Gardner to distinguish 95 percent of the lipsticks from one another, she reported February 22 at American Academy of Forensic Sciences annual meeting. Whether crimson, paprika or plum, or even two closely related reds, the Raman barcodes were unique. Test of lipstick smears on some fabrics weren’t as conclusive: on silk, for example, the lipstick signature was discernible, but on red car upholstery, the signal was lost.
P. Gardner and M. F. Bertino. Evaluation of lip cosmetics using Raman spectroscopy. American Academy of Forensic Sciences meeting, Washington, D.C., Feb. 22, 2013.