There are many surface treatments / coatings available this is just a sample of the common types requested.

Zinc plating – Galvanizing

Zinc electro plating – Clear passivate, yellow passivate, hexavalent chrome free thick film, olive drab passivate, black Passivate

Powder coating – Polyester, Epoxy polyester

Painting – Epoxy,urethane,etch primer,primer, electro static

Blackening – Black oxide

Chrome plating – Hard chroming

Anodizing