Black & zinc is also called galvanized and black passivation or black zinc plating. The black passivation will be performed after galvanizing, aimed to obtain a dark appearance. The anti-rust ability of black & zinc is strong. Black zinc plating is a kind of metal anti-oxidation processing, which is commonly used in fasteners.

Black & Zinc Fastener

Silver nitrate or copper sulfate should be added to the passivation solution as a blackening agent. After the passivation, the product has black and shiny surface and excellent corrosion resistance. The so-called rainbow zinc plating refers to the zinc plating layer, which is treated in chromium acid salt solution once, and  obtained a rainbow-colored passivation film. Generally, the structure of rainbow zinc plating is the complex mixture which composed of basic chromium chromate, basic zinc chromate, chromium chromate, zinc chromate, and oxides of zinc and chromium. The galvanized layer can greatly improve its corrosion resistance when it passed the passivation treatment and became iridescent color. The colorful zinc plating is mainly used for the protection of steel parts. The black passivation film can be used for decoration, matting and solar heat absorption. The film formation mechanism of the black passivation film is basically  same as  the color passivation. The difference is that there are some Ag2O and fine particles of metallic silver in  the reduction products of the black passivation which contains silver salt. The black passivation film contains Cu2O, which is mixed in the passivation film, and makes the passivation film black.

Black & Zinc