Inkless printers use paper with colorless dye crystals embedded connecting the two outer layers of the paper. When the printer is twisted on, heat from the drum causes the crystals to colorize at different rates and become visible. The technology was worked on by Zink Imaging and is now accessible (2007). Because of the way it prints, the printer can be as little as a business card, the images are waterproof, and in fact, one product slated for release by Zink Imaging is a digital camera with a printer built into it. Xerox is also working on an inkless printer which will use a extraordinary reusable paper coated with a few micrometres of UV light sensitive chemicals. The printer will use a particular UV light bar which will be able to write and erase the paper. As of early 2007 this technology is at a halt in development and the text on the printed pages can only last between 16-24 hours before fading.