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What is Black Oxide?

Black Oxide is synonymous with “Black Magic”, “Black Pentrate”, “Black Passivation”, “Bluing” to name a few.

The Black Oxide process is a chemical conversion whereby the finish, the formation of black iron oxide, is produced by a chemical reaction between the iron on the surface of the ferrous metal and the oxidizers which react to form magnetite (Fe304).

Supplementary after-finish treatments will determine the final appearance of the part and increase its usefulness. The choice in after-finish treatment is dependent on the part configuration, application and end-use.

A black oxide finish can be formed in either a hot or cold solution. Universal Black Oxide only utilizes the “hot” black oxide process.


How is the process performed?

There are six fundamental steps for the Black Oxide finishing process:

  1. Clean

  2. Rinse;

  3. Acid Pickling / Alkaline de-scaling (if required)

  4. Black Oxide (parts are submerged in an alkaline salt solution at approximately 285 degrees F.);

  5. Rinse;

  6. Supplemental treatment

Black oxide finishing cannot be produced over plated parts (e.g. zinc, chromium, phosphate). This plating must be stripped prior to the black oxide process.


The benefits of black oxide finishing are:

  1. Aesthetics:  Black Oxide Finishing is visually appealing. The part may exhibit a lustrous shiny or matte black finish depending on the hardness of the metal as measured on the Rockwell scale and the quality of the surface (polished vs unpolished).

  2. Anti-Corrosion Properties: Black oxide finishing with "after-finish" treatments such as oil, wax, or lacquer are designed improve the appearance, abrasion resistance, and corrosion resistance of the part to which they are applied.

  3. Dimensional Integrity: Black Oxide Finishing preserves metallurgy and dimensional integrity of precision components unlike plating or painting.

  4. Durability: Black Oxide Finishing can only be removed chemically or mechanically. It does not chip, peel flake or rub off.

  5. Improved lubrication & Anti-Galling: Black oxide finishing improves lubricity and anti-galling attributes because of the after-finish oil creating smoother running, mating parts.

  6. No Embrittlement:  Hydrogen embrittlement is not a factor in Black oxide finishing as no acid activation is required.

  7. Reduces Reflection: Black oxide finishing reduces light glare and in turn eye fatigue which makes it an excellent choice for moving parts such as hand tools, machine parts and surgical instruments.

  8. White Corrosion Protection: Black Oxide finished parts do not exhibit "white-corrosion" as do some electro-plated parts thus making it an excellent choice for electronic components.  

  9. Weldable: Finishing a part with Black Oxide does not impede its weldability.

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