This guy was tracing patterns on his t-shirt with ultraviolet LEDs. The shirt was absorbing the light and wherever he traced, it would leave a glowing pattern that would eventually disappear. I asked him what he used and he said he used invisible ink. I ordered some invisible ink of my own and tried it on a shirt but the ink wasn't absorbing the light and leaving glowing trails. The only thing it did was glow if I shined the ultraviolet light over it but it would disappear as soon as I moved the light away or turned it off. Does anyone know what the guy used?
