Cupric oxide powder is a glass pigment typically used in soda, lime, and silica glass coloration. Particles size of metal powders plays an important role in the coloration of glasses, the general rule is that smaller pieces of metal and glass need less annealing. In particular, Copper Oxide can give glasses an aquamarine color and the typical amount is 1-3 % of CuO, but if cupric oxide is reduced with a specific thermal treatment, copper-ruby glasses are formed.