Here’s how steel blacking works:-
1. Metal Activation & Surface Preparation
- The steel surface must first be cleaned and degreased to remove oils, rust, or contaminants.
- The potassium bifluoride (KHF₂) acts as an activator/etchant, lightly attacking the steel to create a more reactive surface for the blackening reaction.
2. Oxidation & Metal Deposition
- Copper sulphate (CuSO₄) and nickel sulphate (NiSO₄) provide metal ions (Cu²⁺ and Ni²⁺) that deposit onto the steel surface in a thin layer.
- These ions react with the iron (Fe) in the steel, displacing via a redox reaction.
3. Selenium Dioxide (SeO₂): The Blackening Agent
- Selenium dioxide reacts with the deposited copper/nickel and iron to form a black selenide compound (e.g., CuSe, NiSe, FeSe).
- This creates the deep black appearance (unlike hot bluing, which forms Fe₃O₄ magnetite).
4. Final Sealing (Required for Protection)
- The blackened layer is not corrosion-resistant on its own.
- After rinsing, the part must be coated with oil, wax, or lacquer to prevent rust.
Key Differences from Traditional Hot Bluing
- Cold process (works at room temp or slightly warmed, no boiling or heating of the steel is required).
- Faster (minutes vs. hours for hot bluing).
- Uses selenium for a darker, more uniform black (vs. magnetite in hot bluing).
- Less durable—requires sealing for rust prevention.
The blackened steel items will need to be treated after dipping with dewatering oil, or other form of oil, varnish, lacquer or other barrier to prevent rusting as the black layer offers very little protection from atmospheric attack. Steel Blacking Kits contents: black dipping tank, metal blacking solution (10 Litres), mask, gloves, eye protection glasses, cleaning cloth and instructions.
- Steel blacking kits are not suitable for stainless steel.
- Click here for the instructions.
