Researchers at Xerox have come up with a way to add fluorescent words and images to documents like checks, coupons, and transcripts using standard printers. The technique makes it possible to create everyday documents that have telltale marks visible only under ultraviolet light.

Bright white paper is often fluorescent to begin with; the new process exploits that fact by printing the same shades of color in different ways, leaving more or less paper exposed. For example, in standard color printing, which uses cyan, magenta, yellow, and black inks, a gray tone can be produced with lots of the first three and very little black. But it can also be produced with more black and a little color plus the white of the bare paper, which will fluo­resce under ultraviolet light. The same technique can yield a wide range of shades, each produced by multiple combinations of the four ink colors.

The technology boils down to “finding different combinations of the four colors that present the same visual color but provide very different page coverage,” says Reiner ­Eschbach, research fellow at the Xerox Research Center Webster. The necessary software will be incorporated into high-end commercial printers.