Presto Black® BST4 brush-on liquid is a fast acting, cold blackener for all iron and non-stainless steels. When applied to any clean ferrous metal surface, BST4 blackens within 30 seconds and forms a durable, black finish that can be topcoated to form an attractive, protective black oxide finish.
In the machine shop, Presto Black® BST4 liquid serves as a fast-acting blackener of re-machined areas or reworked metal parts. It is suitable for quick repair for scratches or damaged areas on parts previously black oxide finished.
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