Dark Bronze AnodisingUnited Anodisers operates the Anolok™ process where the colour is developed electrolytically by depositing cobalt metal into the porous film. Increasing the amount of cobalt deposited gives shades of bronze from pale bronze right through to black.

Light scatter produces the colours and this method of production ensures that the colours obtained are completely fade free.


The majority of metals are unsuitable for electro-colouring, the choice being restricted to cobalt, tin or nickel. Although perfectly satisfactory results can be obtained with tin, processing is more difficult to control, particularly in the darker shades. Deposition can grow to the extent where the pores are difficult to seal and deterioration in a short space of time can result. The tin electrolyte is also highly acidic, which can lead to dissolution and increases the risk of poor abrasion resistance.

With a nickel based colouring solution production of dark bronze is difficult and black is impossible. Therefore Anolok™ colouring using cobalt is the safest of all the commercially available bronze anodising processes.


Anolok™ colouring was commercialized in the mid 1960's in Japan. United Anodisers was granted an ANOLOK™ license in 1971 by Alcan International and has processed more Anolok™ bronze anodising than any company in the world outside Japan. Anolok™ is now a registered trademark of United Anodisers Limited.

In 1987 we introduced the Japanese "Unicol" colour matching technology into our colour anodising process. This dramatically improves the colour match piece to piece and is the only unit in Europe.


In addition to the general anodising benefits (see "Benefits") Bronze and black finishes produced by the Anolok™ method using Cobalt have the following advantages over the alternatives:

  • Cobalt deposits evenly with dark colours
  • Cobalt deposits in the bottom 12 microns of the anodic pore
  • pH of the colouring solution does not soften the film
  • QUALANOD specification admittance sealing values can be achieved with dark colours.

Anolok™ Bronze Colour Swatch

The colours shown here are for reference purposes only. Due to different colour renditions on different monitors an accurate representation is impossible. For an accurate metal colour swatch please contact us using the samples request form.

Example Buildings

Gracechurch Street Project
Rivermill House Project
Sanger Centre Project

The World's leading Architectural Anodisers of Continuous Batch, Sheets, Plate, Profile and Specialist Products