phosphating
Phosphating - a chemical or electrochemical process of producing protective matte gray phosphate on metal surfaces; Runs in hot phosphate and phosphoric acid solutions. Phosphate coating is an effective anti-corrosion coating, resistant to high temperatures, very well suppresses light reflections, but is relatively soft. In addition, it reduces friction coefficient and provides a good primer for paints and varnishes. It is also dark gray and black. Can be used both in tool steel and stainless steel knives.