This color-changing ink is called "light-changing ink", which, as its name implies, is optically variable ink. It is an ink containing optically variable pigments. This ink changes color according to the incident angle and visual angle of light, and has a clear two-color contrast effect. It is mainly made by gravure or screen printing. It is internationally known as OVI (Optically Variable Ink)
Danger level: Ink is dangerous mainly because it contains many flammable components, solvents such as toluene, xylene, butanone and so on. Therefore, ink belongs to the third category of dangerous goods, flammable liquids.