Black Oxides


Black Oxide Finish for Steel

Blackon - S is an alkaline salt which, when dissolved in water and heated, will produce a black oxide finish on steel. The oxide finish is normally top-coated and sealed with a rust preventive oil, wax or lacquer to enhance the depth of black and impart corrosion resistance to the finish.

  • Will Blacken a wide range of carbon steels, alloy steels, and hardened tool steels.
  • Lower viscosity solution resulting in reduced drag-out loses.
  • Very concentrated product.
  • Excellent wetting properties, providing a more uniform finish.
  • Produces very little dimensional change (< 0.000005”).
  • Very economical black chemical conversion finish.
  • Black oxide finish has good wear resistance and excellent adhesion.
  • Meets military specification MIL-DTL-13924D Class 1.
  • Tolerant to contamination with copper, colloidal red iron, oxides, zinc, etc.
  • Pleasing decorative black finish.
  • Provides an anti-galling surface.
  • Tanks: Mild steel tanks are required.

  • Heating and Cooling: Gas heating units are preferred for quickest heat up and temperature recovery when a load is introduced into the solution. Electric immersion heaters may be used but care should be taken to avoid scorching the solution by providing enough heaters to evenly heat the solution. 0.317 KW will be required per gallon of solution for a two-hour heat up time.

    An automatic indicating temperature control should be used to control a 1/4 inch electric operated water inlet valve.

  • Agitation: Mechanical agitation should be used during heat up to avoid local over-heating that will produce a loose red oxide on the parts.

  • Ventilation: Required.

    Water must not be allowed to enter tank unless solution is boiling or is being stirred.

    A galvanic cell will be set up between dissimilar metals. Therefore, if dip baskets, hooks, or rotating barrels must be constructed of stainless steel they must be insulated from the mild steel tank.

Required Inventory
  • Blackon - S: Salt used for make up and replenishment.

  • Blackon - S - R: Additive used to control excess iron.

Operating Conditions:
  • Blackon - S: 5.75 Lbs/Gallon (660 g/L)

  • Temperature: 285 – 290 °F (140 – 143 °C)

  • Immersion Time: 5 – 20 Minutes.

  • Solution Loading: 1 – 2 Lbs of parts / gallon including fixtures. (120- 240 g/L)

Make Up
  1. Fill tank half full with cold water. Do not turn on heat.
  2. With the exhaust system turned on, add the Blackon - S salts to the cold water while stirring to dissolve the chemicals. Do not add all of the salts at once as this could cause a violent eruption.
  3. When all the salts have been added and dissolved, add cold water to bring the solution level to within 2 inches of the final desired level.
  4. Turn on the heat and stir as the temperature rises. Do not have the power turned on to the water inlet valve.
  5. When the solution reaches a boil, the motor operated valve may be turned on. If the boiling temperature exceeds 290°F water may be added slowly to lower the temperature. If the boiling temperature is less than 285°, additional Blackon - S salts can be added slowly to raise the boiling point or the solution may be allowed to boil to evaporate water and raise the boiling point. Adding salts, adding water or evaporating water is used to make the final adjustment of the solution to the desired operating level where it is then maintained.
Black Oxide Process:
  1. Clean alkaline soak cleaner.
  2. Rinse.
  3. Acid pickle.
  4. Rinse
  5. Blacken parts in Blackon - S.
  6. Rinse. Transfer time should be as short as possible to avoid the development of a red tint on the metal surface.
  7. Seal the finish in a water displacing solution.

The concentration of Blackon - S is maintained by the boiling point of the solution. The salts are mainly lost from the solution by drag out and must be replenished. Frequent additions of small amounts of salts will produce more uniform results than large amounts added less frequently. Water will be lost only by evaporation.

If the boiling point drops below 285°F (140°C), salts are slowly added until the boiling point reaches 285°F. If the boiling point exceeds 290°F (143°C) water is slowly added until the boiling point is reduced and the heat is lowered to provide a gently rolling boil.

Salts are added only to raise the level of the tank or raise the boiling point. If the solution level falls below the desired working level, water is slowly added until the solution level reaches the desired point, and then the salts are slowly added to produce the desired boiling point.

Water must not be allowed to enter tank unless solution is boiling or is being stirred.

When salts are added to a Black Oxide solution they should be added slowly by sprinkling over the entire surface while stirring the solution. Large additions of salts should never be dumped into the solution as a violent eruption of the hot solution could occur.

Although the temperature of the solution can be maintained by manually adding water, an automatic indicating temperature controller is recommended for the safe addition of water. As water is evaporated, the boiling point will rise and the automatic temperature controller will replenish the water as needed on a continuous basis, maintaining the correct boiling point and concentration.

Water should only be added automatically to the solution when it is boiling so that the fresh water is rapidly and thoroughly dispersed throughout the solution from the boiling action. If water is added to the solution when it is not boiling, a violent eruption of the solution could occur. Stirring the solution is satisfactory if water is added manually when the solution is not boiling.

The bath should be periodically cleaned to remove the accumulation of sodium carbonate, iron oxide and soils at the bottom of the tank. The surface of the solution should also be periodically skimmed to remove hydrated iron oxide from the surface.

Sludge accumulating on the bottom of under fired gas heated tanks could lead to a violent eruption of the solution due to a sudden overheating from the insulating effect of the sludge. The sludge could also become overheated and suddenly crack, allowing water to penetrate below the sludge causing the sudden formation of steam and the violent eruption of the solution.

When heat is applied to a cold Black Oxide solution, the solution must be stirred until the operating temperature is reached to avoid overheating and the violent eruption of the solution.

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