Metal Coloring: Black Oxide, Zinc Colors and Anodizing

Metal coloring isn’t spray paint — it changes the surface color through chemical or electrochemical reactions, so the color bonds in and resists peeling. It splits into groups by metal and process.

Black oxide forms a black magnetite film on steel in a hot alkaline bath, giving a deep black with almost no added dimension (it doesn’t eat thread size) — ideal for screws, nuts, bolts and tools that need looks and reduced glare.

On its own it offers little corrosion protection and needs an oil or wax topcoat. Its strengths are low cost, good looks and preserved tolerances.

Zinc plating colors come from the Cr3+ passivation layer: clear/blue, yellow/iridescent, black or olive drab. These give appearance and corrosion protection together — a popular choice for fasteners (see the Cr3+ zinc article).

Aluminum is colored by anodizing: a porous oxide layer is grown, dye fills the pores, then it is sealed. The result is vivid color (black, red, blue, gold) with a hard, corrosion-resistant surface.

Unlike plating, the colored layer is integral to the metal and won’t flake. It is popular on aluminum parts, hardware and trim.

• Gray-black phosphate — a matte gray-to-black base for paint and oil adhesion.
• Heat/temper tinting — colors (blue, purple, straw) from heat on steel; seen on springs and fasteners.
• Electrophoretic / E-coat — even black color by electrodeposition; high corrosion resistance.
• PVD coating — ultra-thin film colors (gold, rose gold, black) with high wear resistance; premium parts.

For low cost, black color and preserved thread size → black oxide; for color + corrosion in one → colored zinc passivation; for vivid color and a hard surface on aluminum → anodizing. Ask our team to match process to real use.