What is black oxide?

Black oxide is a blend of caustic, oxidizers, and additives that is used on ferrous metals. There are three types of metal blackening: hot, mid, and room temperature blackening. EPi was the first company to offer all three processes.

Hot black oxide (285 F°) is a conventional hot process which produces a true black oxide iron magnetite (Fe3O4) finish. It is a premium-grade salt mixture which will blacken a wider range of steel alloys than any other process on the market.

Mid-temperature black oxide (225–245 F°) is the latest development in blackening processes, producing a true black oxide iron magnetite (Fe3O4) finish. It produces no caustic boiling fumes and provides a safer working environment.

Room-temperature blackening (65–85° F) is the preferred metal-blackening process for safe and convenient in-house blackening. It is an excellent non-bleed black finish for powdered metal and cast iron. It produces super deep blackness and corrosion resistance equal to hot oxide blackeners.

It is important to note this is not a true black oxide process; however, it may be referred to as room-temperature black oxide. Room-temperature blackening processes are autocatalytic reactions of a black selenium-copper compound that deposits on ferrous parts through an immersion process.

What makes EPI’s black oxide and metal-blackening processes better?

Insta-Blak processes do not produce smutty rub-offs like other room-temperature products. Our Ultra-Blak products are premium-grade black oxide, and Kool-Blak does not produce a smutty rub off like other mid-temperature processes. They are easy-to-use with wide windows of operation.

What are the advantages of black oxide and metal blackening?


  • Produces true black oxide finish Fe3O4 magnetite finish
  • Abrasion resistance
  • Corrosion protection
  • Meets military spec MIL-DTL-13924D and AMS 2485H
  • Blackens faster than other hot black oxides
  • Less sludge generation than other hot black oxides, which means lower gas bills


  • Capital costs less than $10,000–15,000 for turnkey operations
  • Energy savings
  • No CO2 emissions or green house gases
  • 1–5 minute process time for blackening
  • Powder metal does not bleed-out white salts like hot black oxide
  • Cast iron and steel castings do not turn red
  • No ventilation costs
  • Provides corrosion resistance
  • Dimensional stability thickness 5–10 millionths of an inch
  • Can be painted over
  • Anti-galling properties
  • Aesthetic appeal
What can black oxide be used for?

Black oxide can be used on a wide variety of metals. Examples of specific products that can be blackened with black oxide are listed below. 

  • Locks
  • Automobile and motorcycle parts
  • Machine parts
  • Power tools
  • Hardware and electornic hardware
  • Architectural applications
  • Furniture
  • Ironware
  • Exercise equipment
  • Large metal sheets
  • Gears
  • Hydraulic and pneumatic components
  • Lawn and garden equipment
  • Candle holders
  • Fasteners
  • Storefronts or displays
Who uses black oxide?

Large companies such as lock manufacturers or auto manufacturers use black oxide on a large-scale basis to blacken metal parts. Black oxide can also be used by the home hobbyist who would prefer to blacken just a few items. Below are some of the major industries that use black oxide coating.

  • Ammunition manufacturers
  • Appliance industry
  • Architectural industry
  • Auto industry
  • Camping and hunting
  • Collars/coupling industry
  • Construction equipment industry
  • Fastener industry
  • Firearms
  • Hardware industry
  • Metal stampers
  • Military components
  • Oilfield Industry
  • Power hand tool manufacturers
  • Recreational vehicle industry
  • Tool & die industry
  • Tube cutters/fabricators
How is black oxide applied?

Hot- and mid-temperature black oxide is applied through a seven-step process.

  1. Clean and degrease metal parts
  2. Rinse metal parts
  3. Hydrochloric acid
  4. Rinse metal parts
  5. Blacken parts in boiling solution (hot: approximately 285 F°, mid: no boiling, 225–245 F°)
  6. Rinse metal parts
  7. Seal and finish

Room-temperature metal blackening is applied through a five-step process.

  1. Clean and degrease metal parts
  2. Rinse metal parts
  3. Blacken metal parts 1–5 minutes at 65–85 F°
  4. Rinse metal parts
  5. Seal and finish

Some steels require an additional prep and rinse, adding two more steps.

What types of metal can you blacken with hot or room-temperature black oxide ?
  • Steel
  • Stainless steel
  • Cast iron
  • Copper
  • Brass
  • Cadmium
  • Zinc
  • Nickel
  • Electroless nickel