Scientists at Xerox have developed an ink that will disappear from printed paper in 24 hours, allowing the paper to be reprinted and reused again. The ‘disappearing ink’ is actually not an ink at all, but a temporary discoloration of light sensitive molecules known as photochromes. A sheet of paper is coated with these molecules (on both sides) which change color in response to ultraviolet light. After printing, the ‘ink’ starts to revert back to its natural state due to heat provided by the surrounding air. The paper itself is no more expensive than a regular page, costing about 0.5p per sheet.

The technology, which will not be commercially available for several years, will reduce the amount of energy required to print a single page by a factor of 200 – from just over 200kJ (which would power a 75W light bulb for an hour) to 1kJ (which would power the bulb for just 18 seconds), Mr Smith said. A recycled page uses about 110kJ of energy.