Black Oxide

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
How to prevent blackened parts from getting rusty?
Customers reach out to us asking how to prevent their freshly blackened parts from rusting. EPi recommends: Use running water to rinse the parts for 1-2 minutes; Do not dry the parts between prepping, cleaning, and blackening; Do not use compressed air to dry the parts as it contains water droplets; Apply E-Tec (see instructions) sealer to extend the life of the finish and protect the surface. One of our customers shared their experience/process with us. After analyzing their process, we concluded that using compressed air for drying the parts may lead to rusting. Below is their process:
  1. Using a cleaning solution on the parts
  2. Rinse in Distilled water
  3. Soak in Black Oxide Concentrate, currently mixing 8 to 1 with Distilled Water
  4. Rinse in Distilled Water
  5. Soak in oil
 We weren’t originally drying the part between each stage, except when we went from cleaning solution to initial rinse. We are now drying each part with compressed air between each stage, but finding similar issues.   Freshly blackened parts The same part overnight The same parts after a week. 
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