Black or dark blue finishing is the application of a noble oxide layer to steels and ferrous materials. Depending on the customer's desires and the nature of the materials, two different processes can be used:
- The parts are immersed in an acid bath at a high temperature to obtain a glossy black surface.
- The parts are often coated with a special tincture, then brushed again to obtain a matt blueish black satin surface. (Often used on older weapons or weapons with several barrels)