Brass is an alloy made by mixing two metals, copper and zinc, in a certain proportion, and has good processing and mechanical properties. In an oxidizing environment, an oxidation reaction occurs on the surface of brass, forming a layer of oxide film. The color of brass after oxidation is mainly dark yellow or brown.

The color of brass after oxidation depends on the thickness and structure of the oxide film. In general, the thicker the oxide film, the darker the color. The main component of brass oxide film is copper oxide, which makes the surface of brass appear dark yellow. In addition, the structure of the oxide film can also affect the color. When the surface of the oxide film is uneven, when light passes through different thicknesses of the oxide film, interference and scattering of light occur, resulting in an irregular brown color on the surface of brass.