Black Oxide Coating

Delivering smooth, long-lasting protection for your metal parts.


Black oxide coating creates a chemical reaction on the surface of a metal part that turns it black.

Why not just paint your parts black? Well, paint is a layer that makes your parts bigger by a few thousandths of an inch. In other words, the paint causes a dimensional change, and even small fluctuations can affect how different parts fit together. Black oxide treatment, by contrast, leaves parts essentially the same size because it’s only a few microns (millionths of a meter) thick.

So, black oxide coating gives you an attractive black finish and a modicum of corrosion resistance. Even better, you don’t have to buy any black paint or worry about the chipping, peeling or flaking of the finish.

That makes black oxide coating a practical, economical way to give metal parts an attractive physical appearance. The process can also be used to reduce glare from a part in applications where that would be beneficial. This reduces glare and eye fatigue for the user.

How black oxide coating works

The point of the black oxide process is to create magnetite (Fe3O4), an alloy of iron and oxygen molecules, on the surface of the metal.

Dipping a metal part into a heated, alkaline liquid for a specific period of time triggers the chemical process that forms magnetite on the part’s surface.

Yes, that means black oxide is a kind of rust (it’s black instead of red). But it’s done under controlled circumstances that add corrosion resistance to the metal part instead of causing it to decay.

What kinds of parts get black oxide treatment?

Because black oxide is mainly for aesthetic appeal, it’s rarely used on parts most people never see. But metal parts people can see — and especially hold in their hands — may be good candidates for black oxide, which is common in:

  • Firearm components like barrels and stocks.
  • Hand tools like wrenches and crowbars.
  • Nuts, bolts, screws and washers in products people assemble themselves.
  • Under-the-hood engine parts like pulleys and hood braces.

This short list just scratches the surface of the many applications of the black oxide process. Basically, if you want a product to have an aesthetically pleasing black exterior, this process is one of the most practical ways to get it.

The Paulo approach to black oxide coating

At Paulo, we depend on a rack-and-barrel approach to black oxide processing. Using both barrels and racks means we can treat parts of pretty much any size.

And we can fully customize the process. If your parts need additional treatments after the dip, we can make that happen too. The result is you get the attractive black finish you want without worrying about any of the performance issues that may arise with a paint finish.

With decades of experience in treating metal parts and computerized processes to ensure accuracy and hold costs down, we can ensure your parts meet the most demanding specifications and industry standards.

See how our Paulo metal finishing services can help you.

Contact us.