Share About a decade ago, Romain Testuz, a student at the Swiss Federal Institute of Technology in Lausanne, grew fascinated by “the possibility of controlling light,” he says. Under the guidance of a professor, he began to experiment with algorithms that could alter the way light is reflected on a surface. What started out as a theoretical effort became practical in 2016, when Testuz cofounded Rayform, a technology company that works with luxury makers to “sculpt light” on nearby surfaces, often as an anti-counterfeiting solution. In September 2019, Testuz and his business partner, Yuliy Schwartzburg, parlayed the technology into a jewelry company called The Rayy, which makes a range of minimalist, unisex rings and pendants that can be customized to reflect sunlight into a personal message. The technology is based on an optical phenomenon known as caustics: “the effect you see when there’s sun at the bottom of the sea or a swimming pool, those beautiful abstract patterns of light when light passes through a wavy source of water,” Testuz says. “That’s the source of this project—concentrations of light that come through curved surfaces.”