// Anodising

RSC are Anodising specialists in the South-West. Find out more about our anodising services and get in touch for advice and quotations.

Sulphuric Anodise

Sulphuric anodising is an electrolytic treatment for aluminium that produces a coating of aluminium oxide. This coating exhibits excellent corrosion resistance and can be dyed in a variety of colours.

The coating is available up to around 25 microns in thickness (beyond this thickness, hard anodising is required). Clear (natural colour) coatings are typically 5 to 15 microns and dyed (coloured) coatings are typically 10 to 25 microns.

Thickness & Growth:

Anodising is an electrolytic conversion coating, it transforms aluminium on the surface of components into aluminium oxide. Since aluminium converts rather than deposits, some of the thickness of the coating is ingress into the material and some of the thickness is growth out of the material. A good rule of thumb is that 50% of the anodic film is below the original surface and 50% is above. A part that is anodised with a coating thickness of 10µm per surface would only have about 5µm of growth per surface.

Corrosion Resistance:

Anodised aluminium shows high corrosion resistance in aggressive environments. All of our Sulphuric anodising exceeds 336 hours of neutral salt spray testing to the requirements of ASTM B 117.

Dye Available:

  • Black
  • Grey
  • Blue
  • Red
  • Others available on request


  • Dichromate Seal
  • Nickel acetate seal
  • Hot water seal
  • Cold Seal Nickel Fluoride

Non-Hexavalent Sealing Option:

  • Surtec 650 impregnation and hot water seal

Specifications Covered:

  • NGPS 258
  • MIL-A-8625F
  • DEF STAN 03-25
  • WHPS 258
  • BS EN ISO 7599
  • THALES 16262727-024

Chromic Anodise

Chromic acid anodising process gives relatively soft, thin coatings, normally of two to five microns thickness and is light grey in colour.

  • These are used mainly for electrical insulation and general protection against corrosion under mild conditions sealed for protection against contamination.
  • Unsealed coatings are used as a ‘key’ for paints and adhesives.
  • Chromic anodising exceeds 336 hours of neutral salt spray testing to the requirements of ASTM B 117.

Specifications Covered:

  • NGPS 77
  • AWPS003T
  • DEF STAN 30-24
  • MIL-A-8625F

Hard Anodising

Anodising is the process of extending the naturally occurring oxide layer so as it becomes much thicker and adds increased wear & corrosion protection. Hard Anodising produces a thicker coating with a denser structure and may be preferable for applications where wear, abrasion and erosion are present.

Hard Anodising produces much thicker coatings between 25 and 100 microns and it’s important to remember that Hard Anodising forms both above and below the surface of the component, so may affect critical dimensions.

Where Natural Anodising may be used for aesthetic applications, Hard Anodising is largely a functional process and tends to be darker in colour.


  • DEF STAN 03-26
  • BS EN ISO 10074
  • AMS 2469

Titanium Anodising

Titanium anodising is a process in which titanium oxides are artificially grown on top of an underlying titanium base metal using electrolysis.

The dyeing process is not required with titanium because of its oxide film which refracts light differently than most other metal oxides. By varying the voltage applied during the adonisation process the colour of the titanium surface can be controlled. This allows titanium to be anodized to almost any colour that one can think of.


  • ISO 8080
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