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Burnishing involves immersing ferrous components in a boiling, alkaline-oxidising solution.  During the process black iron-oxide layers form on the surface of the components.  The black tone is dependant on the quality of the material, the surface finish and the composition of the burnishing bath.

Burnishing involves the formation of a surface layer which has a smooth, structureless black appearance, that has considerable resistance to flexing and abrasion.  The boiling temperature in burnishing lies between 133 °C and 144 °C.

According to DIN 50938 a distinction is drawn between one-, two- and three-bath burnishing.

It should be noted that burnishing does not affect the conductivity or magnetic properties of the starting material (steel, iron)


Suitable Materials

All lightly alloyed construction steels and heat-treatable steels (e.g. C60, C45, 42CrMo4, 34CrNiMo6)

Advantages of Burnishing

  • Lower distortion
  • Increased corrosion resistance
  • „Attractive black“ surface
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