Black Oxide, also known as Black Penetrate, Black Magic, Black N, and Gun Bluing, is a unique finish that has special properties which make it the perfect choice for a wide variety of purposes.
A great choice as a metal finish for things like fasteners and automative parts, black oxidizing provides corrosion resisance, reduced glare, decorative finishing, and other benefits. Black oxide doesn't cause dimensional change or affect conductivity. It also makes your parts immune to hydrogen embrittlement.
Black Oxide is a conversion coating that's produced by dipping metal parts into a specially formulated solution at specific temperatures. The chemical reactions that occur, combined with a controlled process of adding water are what ultimately create the best black oxide finish. The entire black oxide finish process is defined as a product of multiple steps, from cleaning, washing, creating the finish, washing again, and eventually applying an after-finish or coating. If you're looking to get black oxide finishing on plated parts (zinc, nickel, chromium, cadmium, phosphate), you have to consider that the plating must be stripped off before the black oxide process.
At Pro-Tec Metal Finishing in Chicago, Illinois, we have a process line of hot black oxide that's used to produce a true durable black oxide conversion coating on steel, stainless steel and copper alloys. From the black oxide process, these essentially dimensionless coatings create very decorative, highly durable black finishes that leave an absorbing oxide layer for oils and waxes that will provide for enhanced corrosion protection.
Applying Hot Black Oxide for stainless steel involves using a mix of caustic, oxidizing, and sulfur salts. Generally, it's applied to 300 and 400 series, and the precipitation hardened 17-4 PH stainless steel alloys. It can be used on cast iron and mild low-carbon steel. This process complies with military specification MIL-DTL-13924D Class 4 and provides abrasion resistance.