Are you tricking us here? It’s a secret! For proprietary reasons, we can’t divulge anything about our products or technology on a molecular level or about the formula itself. However, we can say it’s made with photochromic dyes, which are synthesized of organic materials.
Photochromic dyes are typically invisible to the human eye until they’re irradiated by ultraviolet (UV) light (mostly in the 320-400 nanometer range). The peak wavelength (365 nanometers) is commonly referred to as black light.
Upon such irradiation, the dyes undergo a molecular excitation transition, shifting their energy into the visible range of the spectrum. The reaction is reversed by the absence of UV light, so the dyes either won’t go clear again or they’ll take a long time to become invisible if the temperature is below 50°F, even after the UV light has been removed.