THE novelty is wearing off those birthday cards that play a tinny song. So
how about a picture that changes when you open the card? A new ink that changes
colour when a voltage is applied to it could make that possible, says John
Reynolds, a chemist at the University of Florida in Gainsville.
The polymer-based ink is cheap enough to be printed onto packaging or
interactive business cards, says Reynolds. A tiny watch battery will deliver the
power needed to change the shape of the molecules in the dye, making it
transparent. It retains its new shape until the…
