Copper(I) oxide or cuprous oxide is the inorganic compound with the formula CuO. It is one of the principal oxides of copper, the other being copper(II) oxide or cupric oxide (CuO). Cuprous oxide is a  red-coloured solid and is a component of some antifouling paints.  The compound can appear either yellow or red, depending on the size of the particles. Copper(I) oxide is found as the reddish mineral cuprite.