Glow in the dark GDV, GDI or GID Sand, Large Grain Crystal is made from the purest strontium aluminate doped europium. There are 4 main daytime neutral or invisible colors Green, Aqua, Blue and Lilac and there are over 11 Day visible glow in the dark colors. These are the largest grain we can produce at between 1-2mm, has the strongest and longest glow times and the highest charge and discharge rate of any of the phosphorescent pigment powders.