Black Phosphate
Parts are immersed in or sprayed with a phosphoric acid and phosphate salt solution which chemically reacts with the surface to create a layer of crystalline phosphates. This chemical reaction also blackens the surface of the part. Black phosphate is a common surface preparation for further coating or painting as it is porous with excellent adhesion.
Application: Standard finish for drywall screws, however this finish is most commonly used as a pretreatment for further plating.
Appearance: Dull grayish black.
Black Phosphate & Oil
The addition of oil offers mild corrosion protection, added lubricity, and can prevent galling.
Application: Standard finish on floorboard screws, frame bolts, and toplock nuts (that aren't zinc plated) due to added lubricity.
