The underlying principles are similar to those used in transitional eyeglass lenses. Credit: Carson Bruns et al.

Tattoos are pretty permanent decisions , and laser removal is often described as more painful than actually getting them in the first place. But what about a design that can only be seen when you want to see it? Engineers at the University of Colorado Boulder are working on a new type of tattoo ink to answer that question. Their dye is specifically concocted to physically alter depending on exposure to visible or ultraviolet (UV) light.

The team described their invention in a study published earlier this month in the journal Matter & Light , and they didn’t only demonstrate the capabilities in the lab on silicone and pig skin.…