General Informations

General Informations


Blacking means the black colouring of iron surfaces by immersion the components in acid / alkaline solutions or fused salt. It deposits mixed oxide coatings (conversion coatings) of FeO and Fe2O3 in a deep black colour. As a result of the very thin conversion coating (ca. 1 µm) the components are dimensionally stable. Because of porosity of the coatings the corrosion protection is very low. Oiling or greasing will improve the protection a lot. The coatings are extensively bend- and abrasion-proofed. There is a resistance against temperatures up to 300°C. The conductivity and magnetic properties of the base material (steel, iron) will be in no way affected.

Blacking is mostly applied by the metal working industry. A sub-group is the blacking of small arms.

The blacking at room temperature or Cold Blacking is a system without the disadvantages of the conventional hot blacking. Disadvantages are:

  • High energy consumption for the heating of the bath (133-145°C)
  • Handling of dangerous, toxic and aggressive chemicals (acids, lye's, salt solutions)
  • Disposal of contaminated waste
  • Very strong heating of the blacking solution to prepare (heat of blacking salt solution). And the risk of splashing and the delay of the boiling point
  • The regeneration of an occupied bath is not possible because unresolved blacking salt will contaminate the base material
  • Very slow dissolving of the blacking salt. Unresolved salt will provoke an accumulation of mud in the bath
  • High packing and transport costs because hot blacking is only in large, industrial plants possible
  • A lot of effort for ventilation and observation
  • Long immersion times 

The advantages of NU-BLAK® blacking at room temperature in contrary to the conventional method:

  • simple immersion operation (result in five steps; time for the blacking: 1 minute max., no ventilation required)
  • completed in-house production – no transport and packing costs
  • Inexpensive equipment
  • high covering power (1 litre concentrate, dilution 1:3 for about 8-12 m2) depending on the base material 
  • energy saving (no heating costs)
  • material saving (long-term storage, solutions do not collapse)
  • uniform black colouring of all treated parts (polished or rough surfaces, threads or holes
  • no dimensional alternations, no moving
  • no efflorescence of salts (= no white leach out)
  • black colouring achieved by chemical structural change (conversion)
  • no discharge problems
  • Filter system for the rinse water – rinse water can be let into the sewer
  • no acids or lye's
  • no hydrogen embrittlement
  • no red spots etc. on casts