How can you print without ink?

Technology seems to have come full circle since the invention of ink some 4,000 years ago. Although the printing press, an efficient way to apply ink to paper on a mass scale, was one of the most important technological advances in the history of humanity, taking ink out of the equation can simplify modern printers.

Take, for instance, the thermal fax machine. This useful gadget merely needs to apply heat to special thermal paper to print text or images. Without the mechanisms that ink requires, the printer is simpler, more durable, cheaper to maintain and takes up less space than ink printers. A different type of thermal fax machine uses ribbon rather than ink and melts the ribbon to paper to print text. Read How Thermal Fax Machines Work to learn more about this process.

Conventional photocopiers actually don't technically use ink either. If you've ever maintained a photocopier or read How Photocopiers Work, you know that they use a dry, powdery material called toner. The toner is negatively charged, and the copier uses static electricity to print copies. The copier uses light to measure the print on the original and assembles the powdery toner to fall to positively charged areas to replicate the text or image. It then fuses the toner to another piece of paper to make a copy.

Thermal fax machines and photocopiers are far from cutting edge and haven't come close to replacing ink. Despite their availability, people still prefer the sharp look and durable quality that ink printers produce. Nevertheless, scientists are now developing several other fascinating printing processes that might give ink a run for its money.

One company, Zink (which stands for zero ink), announced in 2007 that it has perfected a technology for printing without ink. Using embedded dye crystals in the paper, a printer merely needs to apply the right amount of heat to bring those crystals alive and produce a quality print -- even photos. Because there's no need for ink, this special paper allows printers to be exceptionally small. For its debut, Zink partnered with Polaroid, the company that pioneered instant film, to make an ink-free instant mobile photo printer, which isn't much bigger than a pack of cards.

Xerox, the company with the name that's synonymous with photocopiers, is also developing an inkless printing method. But the process it's working on is radically different from predecessors. Inkless prints aren't known for their long-lasting durability, but Xerox is turning this drawback into an asset. In fact, they're intentionally working to make inkless prints easily erasable. Although this seems counterintuitive, it makes a lot of sense for several reasons.

In offices, many people print papers to use for just a day or even less. To make this practice more economical and environmentally friendly, Xerox is developing paper that doesn't require ink and is completely reusable. It works this way: Xerox first coats paper in heliochromic chemicals. These chemicals darken when the paper is exposed to ultraviolet light (UV). They're similar to the chemicals that cause certain sunglasses to darken in the sunlight and gradually lighten again in dim light. The printer, then, merely "prints" by zapping the paper with the right wavelength of UV light and in the right places. The print can be used and then immediately erased by applying another wavelength of light. With prototypes of this technology, the print automatically fades 16 to 24 hours after printing. But Xerox is working to extend this time period. Ideally, the text will last until the user is ready to erase it manually.

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