How Oxide Painting refers to a technique of glazing in which metallic oxide washes are painted on top of product to achieve color changes and create patterns.

CuO

Copper II oxide is an active metal that combines easily with oxygen, which means that it is very sensitive to oxidation and reduction atmospheres. It produces a very wide range of colors in glazes, from greens (delicate light greens to turquoise to deep emerald green), to red, pink, blue, black, yellow, and copper luster.
Cuprous oxide, Cu2O, has been known as a semiconductor material since the 1980s and has received attention as a viable photocatalyst due to its advantageous bandgap energy of approximately 2.0 eV. However, Cu2O is limited by its stability under irradiation. Cu2O is prone to photo-degradation into Cu metal.
Cupric oxide gives a distinctive series of blues, cuprous oxide a series of greens, and, in the presence of an excess of carbon monoxide (which the Chinese achieved by throwing wet wood into the kiln), cupric oxide yields a bluish red.

All pigments for ceramics are intermixable so why not get creative and experiment by missing your own completely fresh color. During the firing process, the colors fuse extra vigorously creating purity, intensity, and brilliance. The colors are stronger, therefore, significantly less percentage is needed to create vivid colors making them excessively cost-effective.

How to use Copper Oxide in the pottery:

Copper glazes are often used in soda and salt firings because the introduction of volatile sodium during the firing turns copper glazes into various shades of blue/turquoise/green. Sometimes potters use high amounts of copper (10%) in a green salt glaze, which turns black, but when the salt fumes hit that part of the pot, the area turns deep green on one side with the other side of the pot fading to black.
When using ceramic pigments in glazes, usually in concentrations of 1–10%, a little more care must be taken because some pigment systems react with materials in a glaze.