How does the process take place?

It is done by immersion in an aqueous solution at 130 °C with specific chemical agents suitable for oxidizing the nickel and chromium salts contained in the stainless base material.

The process is relatively quick, with dwell time of about half an hour. This is followed by rinsing, drying, and usually oiling, which gives a shinier, more uniform appearance.

Blackening does not impart any special passivity qualities to the treated stainless steel, so improvements in corrosion resistance should not be expected. Depending on the weight and geometry of the workpiece, machining can be done by roto-barrel or basket. In order to give the fasteners and their nuts, a controlled coefficient of friction, it is possible to perform an anti-friction product by immersion and centrifugation that can leave on the surface of the parts a very thin layer, around one micron, of material that can give a better coefficient of friction.