Thinking about forging a check? Might want to reconsider. It just got a whole lot easier to track you down. Using a new application of a recent technology, forensic specialists can figure out when a check was signed, what pen was used and even the origin of the ink used to sign it. Until now, ink could only be traced if a piece of the document were soaked in certain solutions. But the new method, aptly dubbed DART (for direct analysis in real time), can read the ink chemistry off the paper in a few seconds, without leaving any evidence that the paper was examined.

The DART technology, commercially marketed by the Japanese company JEOL Ltd., is a few years old and is currently used by agencies like the FBI to identify minute amounts of toxins. Now, chemists at Ames Laboratory and Iowa State University have adapted this technique to analyze ink samples through mass spectroscopy.

"The writing [sample on paper] is ablated with warm jets of energized atoms like electronically excited helium, which pull off different molecules in the ink," Ames chemist Roger Jones explains. Mass spectroscopy is then used to analyze the molecules trapped in the jet, which detects the masses of all the molecules in the stream. To get their chemical "fingerprints," they are compared with a table of masses of known molecules. The technology can tell molecules apart whose masses differ by only 0.003 to 0.004 the mass of a hydrogen atom (or six to eight times the mass of an electron). The range of detectable masses is also fairly broad, ranging from molecules as light as 70 to 90 daltons (atomic mass units) like benzene, to as heavy as the antibiotic erythromycin, weighing in at above 700 daltons.

Besides identifying many of the solvents, resins, lubricants and dyes in the ink sample, the spectrum also reports their relative amounts in it, a measurement that is used to identify the ink itself from another table of known compositions. "The spectrum of a Bic Velocity is completely different from the spectrum of a Bic Round Stic," Jones says about the specificity of ink signatures. Signatures not only vary by pen model but may even differ from batch to batch within the same line if quality controls are not very stringent. Ink in the same pen model made in eastern Europe before the 1990s, for example, varied from factory to factory, making it possible to pinpoint each pen's origin geographically.

Currently, the chemists are building up a library of ink signatures by using more than 8,000 writing samples archived by the U.S. Secret Service. Once built, this library will provide forensic scientists with a much faster and nondestructive alternative for analyzing documents over current solvent-based methods.