Birchwood Casey’s Presto Black BST4 brush-on liquid is a cold blackener for iron and non-stainless steels. When applied to any clean ferrous metal surface, the solution blackens within 30 seconds to form a finish that can be topcoated to form a black oxide finish.
For machine shops, the solution is useful as a fast-acting blackener of re-machined areas or reworked metal parts, the company says. It can be used as a quick repair for scratches or damaged areas on parts that were previously black-oxide finished. For such applications, users degrease the surface with a cold solvent wipe of alcohol, acetone or lacquer thinner before applying the solution with a sponge or swab. When the surface has turned sufficiently black, the liquid is rinsed of with cold water. A water-displacing, rust-preventative oil is then applied for corrosion protection.
The resulting finish blends well with existing black-oxide finishes and will withstand the same degree of salt-spray exposure, the company says. Available in 1- or 5-gallon containers, the solution can be applied to any type of tool steel in tool rooms, inspection or main production areas.