Birchwood Technologies’ Presto Black BST4 brush-on liquid blackens within 30 sec. of being applied to a clean ferrous surface. The cold blackener can be used on all iron and non-stainless steels and forms a durable black finish that can be top-coated for a protective black oxide finish. According to the company, the blackener serves as a manual black oxide process for brush-on needs and can be a quick repair for scratches or damaged areas on parts that were previously black-oxide finished. The liquid can be used for rebuilding processes on pistons, bearing, crankshafts, and re-machining areas or reworked metal parts, and applications include aerospace and machine shop touch-ups.
The surface to be treated is degreased with a cold solvent wipe or a detergent wash, and then the liquid is applied with a sponge or swab. When the surface has turned sufficiently black, the liquid is rinsed off with cold water and a water-displacing, rust-preventing oil is applied for corrosion protection. The resulting finish has a black color that blends with existing black oxide finishes and will withstand the same degree of salt spray exposure as the original finish, the company says.