C 2732 (OTTO) Copper(I) oxide powder, ≤7 μm, 97% Cas 1317-39-1 - used as a pigment, a fungicide, and an antifouling agent for marine paints. Copper(I) oxide is also responsible for the pink color in a positive Benedict's Test.Cuprous oxide is the inorganic compound with the formula Cu2O. It is one of the principal oxides of copper. This red-coloured solid 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