Researchers at Xerox have come up with a way to use standard printers to add fluorescent words and images–analogous to ID marks on currency that are visible only under ultraviolet light–to ordinary documents. The technology could make it inexpensive to add hidden codes to documents like checks, coupons, and transcripts.
Invisible ink: A new process from Xerox allows commercial printers to print fluorescent words and numbers on documents using standard toner on ordinary white paper. The process, which leverages the fluorescence that already exists in many kinds of white paper, selectively exposes or covers the paper using different color combinations to arrive at the same shade.
Traditionally, a special printer is required to add fluorescent ink, which shines brightly when exposed to ultraviolet light. The new technology creates fluorescent codes with standard printing equipment.
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The secret: leveraging the fluorescence already present in white paper. Many paper manufacturers add fluorescent chemicals to enhance the apparent brightness and whiteness of their products. The new printing technology uses different color combinations to produce the same apparent shade, but some combinations leave more paper exposed.
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Consider a simple black-and-white document. To print gray, you can either coat the paper’s entire surface with a gray-toned ink, blocking the surface completely, or you can print finely pixelated black. To the eye, both strategies would make the document look gray. But with the second approach, more bare paper would be left exposed; this would fluoresce when exposed to ultraviolet light.
Doing this with colors is trickier, but the same principle applies. Working with the four-color printer language of cyan, magenta, yellow, and black, it is possible to create the same shades with different combinations that leave more or less paper exposed. In effect, the printer can “write” fluorescent letters and numbers by simply using different mixtures to produce the same shades. Digital controls on commercial printers make it possible for people to use the same printer to do so, simply by altering the software that controls the color combinations employed in the printing process.
“That is the main trick: every color you see is produced with four basic colors,” says Reiner Eschbach, research fellow at the Xerox Research Center Webster, in Webster, NY, who developed the technology. “Now you have to be in that four-dimensional space, finding different combinations of the four colors that present the same visual color but provide very different page coverage. It gets really complicated to get those combinations, and we need to get the combinations better and better.”
The company says the fluorescent printing system will only be incorporated into high-end commercial printers.
The need for better technologies for document security is large: every year, U.S. companies lose more than $650 billion to fraud, and more than two-thirds of that sum is lost to counterfeiting and document fraud, according to the Association of Certified Fraud Examiners.
“We are turning the problem upside down,” says Eschbach. “Normally, you add fluorescent ink to put on top of the paper. We said, ‘This is messy, cumbersome, costly, complicated, so let’s use the inherent fluorescence in the paper and modify the way we print.’” He adds that the technology will be good for “simple things, like how to protect a coupon or a contract. How do you protect a university transcript? Now you can protect those.”
