Black Oxide Basics

 

What is Black Oxide?

Black oxide is a term used to refer to a coating process. Blackening, oxidizing, black passivating, black oxidizing, gun bluing are all terms referring to the conversion coating or the process for the coating that’s applied to ferrous materials, stainless steel, copper and copper based alloys, powdered metal, zing, and other materials. Black oxide’s primary and most common purpose is to add corrosion resistance, to enhance appearance of parts, and to minimize reflection of light.

Black oxide can also provide a maximal degree of corrosion resistance if it’s impregnated with wax or oil. With minimal building, black oxide finishes are a popular solution.

 

Black Oxide Metal Finishing

The black oxide coating comes about through a chemical reaction between the ferrous material’s iron content and the oxidization salts that are in the black oxide chemical solution. Depending on the specific application, variations of the primary black oxide solution are used. For example, applying hot black oxide for stainless steel involves using a mix of caustic, oxidizing, and sulfur salts. The pieces that will get the coating are usually dipped into a series of tanks such as alkaline cleaner, water and caustic soda at 140.5 °C (the blackening compound), all before the sealant, which is most commonly oil.

 

Post-Treatments with Wax or Oil

Wax or oil post treatments are frequently used for black oxide coatings. When the post treatment material is properly applied to allow for full absorption by the black oxide coated parts, an increased level of corrosion resistance is achieved. It also creates a deeper, darker black appearance. According to Pro-Tec Metal Finishing in Chicago, Illinois, a correctly applied hot black oxide will provide benefits that other coatings don’t. You can read more about Pro-Tec’s process at black oxide finish. You can also find additional information on the Wikipedia page for black oxide.



 

Other Processes

Other types of black oxide processes include mid-temperature black oxide and cold black oxide. However, the exact type of black oxide you choose will depend on your parts and what application you’ll be using them for.


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