PRESTO BLACK BST4 brush-on liquid from Birchwood Casey Co. is an instant acting cold blackener for all iron and non-stainless steels. When applied to any clean ferrous metal surface, the BST4 solution blackens within 30 seconds and forms a durable black finish that can be top coated to form an attractive, protective black oxide finish.

For the Aerospace Industry, PRESTO BLACK BST4 liquid serves as a fast-acting blackener for rebuilding processes on pistons, bearings, crankshafts and re-machined areas or other reworked metal parts. It's for use in prototype and re-machining applications and also serves as a manual Black Oxide process for simple brush-on needs.

In the machine shop, PRESTO BLACK BST4 liquid serves as a fast-acting blackener of re-machined areas or reworked metal parts. It's a quick repair for scratches or damaged areas on parts previously black oxide finished. For these applications, just degrease the surface using either a cold solvent wipe (alcohol, acetone or lacquer thinner) or a detergent wash, and then apply the BST4 liquid with sponge or swab and allow it to work.

When the surface has turned sufficiently black, the liquid is rinsed off with cold water and a water displacing rust preventive oil is applied for maximum corrosion protection. The resulting finish has a good black color that blends well with existing black oxide finishes and will withstand the same degree of salt spray exposure as the original black oxide. The PRESTO BLACK BST4 liquid can be applied to any type of tool steel in the tool room, inspection or main production areas.