JMarshall writes: A new, elastic silver ink allows stretchy circuits to be drawn using a regular pen. Unlike previous inks, which have been made with silver nanoparticles and are prone to clog pens over time, this ink begins as a silver salt mixed with adhesive rubber (abstract). After writing, the ink is brushed with a formaldehyde and sodium hydroxide solution that reduces the silver ions to conductive silver nanoparticles. Researchers strung 14 LED lights together using the ink. The lights stayed lit even through stretching and bending the rubber sheet the circuit was drawn on.