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Sulphuric Anodising

Sulphuric Anodising is type of electrolytic metal finishing treatment that produces a translucent oxide coating. This oxide compound becomes integral to the metal and provides excellent corrosion resistance. Commonly used for conversion coating of aluminium and its alloys, it can also be applied to other non-ferrous metals such as titanium. Available up to around 25 microns in thickness with hard anodising available for thicknesses beyond this.

Why choose Sulphuric Anodising?

  • Anti-corrosion properties
  • Cost effective
  • Wide range of colours available
  • Resistant to scratches
  • Coating thickness of 5-25µm
  • RoHS & REACH compliant

Why choose
MP Eastern?

  • Certified to AS 9100 Aerospace & ISO 9001 Quality Management
  • SEA Member
  • IMF Sustaining Member
  • Free local transport
  • Nationwide courier transport
  • Free Certificates of Conformity
  • Certified to ISO 14001 Environmental

Our Sulphuric Anodising specifications

  • BS EN 7599
  • BS EN 2284
  • AMS 03-25
  • MIL-PRF-8625F Type II

Our Turnaround Times

  • Standard Turnaround is 7-10 working days
  • Express Turnaround is available for additional charge

How to Order Sulphuric Anodising

When specifying anodising we recommend referring to published standards wherever possible. Most standards will require you to provide at least the following information to us:

  • The specification reference, film thickness and sealing requirements
  • The grade and temper condition of the material
  • The significant surfaces and areas where measurements of the coating thickness are to be made
  • Any areas that must not be used as contact points for jigging (or areas that are to be used)
    It is necessary to carry an electric current to the part during processing, these contact areas will remain uncoated, typically parts are located on jigs using holes, bores, tapped holes or along edges
  • Any special inspection and test requirements
    The default inspection procedures for most specifications include for visual inspection and coating thickness measurement, if it is necessary to carry out other inspection procedures by batch or order then generally these have to be specified in the contract or order
  • Any special packing requirements

 The grade and condition of the aluminium have a significant effect on the final product.

Feel free to get in touch with your requirements or for technical advice.

Our Specifications & Standards

We soft anodise to the following standards:




BS EN 7599

Sulphuric acid anodising
Film thickness is specified by referring to a specific class with the following minimum average thicknesses:
Class AA5 – 5 µm
Class AA10 – 10 µm
Class AA15 – 15 µm
Class AA20 – 20 µm
Class AA25 – 25 µm
Surface preparation before anodising is designated by the symbols E0 to E8.
Sealing either hot water or nickel sealing as specified.

BS EN 12373-1
BS 1615

BS EN 2284

Sulphuric acid anodising
Class A – Unsealed anodising
Class B – Sealed anodising
Thickness class 1 – 12 to 25 µm
Thickness class 2 – 6 to 12 µm
We no longer provide dichromate sealing.

Aerospace series

AMS 03-25

Sulphuric acid anodising
Unless otherwise stated on drawing or order film thickness 8 to 13 µm, items that are to be dyed black may have a coating thickness <= 25 µm.
Sealing by hot water seal.
The default sealing option is Dichromate Seal but we no longer offer this as it is classified as a SVHC under REACH so can only be used for Aerospace & Defence applications under authorisation.

Def Stan 03-25
Def 151 Type I


Type II – Sulphuric anodising
Class 1 – Undyed
Class 2 – Dyed
Thickness as specified, sealing various methods permitted unless special or specific sealing processes are specified.


We also hold a large library of customer-specific, superseded and legacy specifications. Please contact us with your requirements.

Guide for Design Engineers

Thickness and Growth

Anodising is a conversion coating which transforms the surface of aluminium into aluminium oxide. As a conversion rather than deposit process, there is both ingress and outgrowth of the material to form the coating thickness. The end result is approximately half of the anodic film below the original surface and half above.

Minimum thickness requirements are specified in the anodising standards but our customers find it easier to specify a thickness range.

Anodising grows at right angles to the surface and where this growth meets at external sharp corners the coating can spall. Thicker hard anodised surfaces are susceptible to this spalling so corners should be radiused as much as possible.

The material has a significant effect on the final appearance and performance of the coating – different grades and temper conditions require different processing conditions. Different grades of alloy are not usually mixed during a process run.

Corrosion Resistance

Anodised aluminium has excellent anti-corrosion properties even in harsh environments. It will however be vulnerable to alkalis and some acids, our technical specialists will be able to provide guidance and assist with testing compatibility.


Anodic films are naturally porous, this allows them to be dyed. Most sulphuric anodising is sealed and this is our default process. For most applications, the most economic and most suitable sealing method is either cold sealing or hot water sealing. Good sealing is crucial to corrosion resistance and is necessary for light-fastness on dyed coatings.

A minority of sulphuric anodising is left unsealed. This is usually when it is going to be painted or bonded. Leaving the anodising unsealed provides a good key for painting.

We provide the following sealing options:

  • Hot water seal (boiling seal)
  • Nickel acetate seal
  • Nickel fluoride seal (cold seal)
  • PTFE seal

Colour Anodising

To achieve a colour finish, a dye is usually used. The pores in the coating absorb the dye and a sealant is applied to lock in the colour. The vividness of the colour will depend on the thickness of the coating. Light colours can be achieved with thin coatings but deep colours usually require a greater thickness.

Our standard dye colour range includes:

  • Black
  • Gold
  • Blue
  • Red

The colour of the clear anodised film and shade of a dyed coating are influenced by the composition of the aluminium from different alloying agents in the base material, colour of the anodised film, film thickness and surface finish and texture from different machining methods.

Wear Resistance

Aluminium oxide has an improved hardness compared to bare aluminium, this makes it resistant to scratching and abrasion. Where wear resistance is a serious concern, hard anodising is the preferred alternative. For situations where low friction is desirable, we can apply a PTFE seal.

Alloy Selection

The most common alloys that we see are 6061, 6082 and 6063. For decorative or cosmetic work, our preferred alloy is 6063, although 6000 series are usually suitable. For non-decorative work, generally alloys in the 1000, 2000, 5000, 6000 and 7000 series are suitable. Please contact us for more information or advice.

Our Tank Sizes

Length 2000mm x Width 400mm x Depth 800mm x Lifting 125kg

Safety & Environmental Compliance

Our sulphuric anodising service is compliant with RoHS (Restriction of Hazardous Substances) & REACH (Registration, Evaluation, Authorisation of CHemicals).

Environmental awareness is part and parcel of our business ethos. We have an active policy of using greener alternatives to the traditional processes. We have held a Environment Agency IPPC permit since 2005 and are regularly audited as part of our ISO 14001 certification.

Laboratory Analysis

Our laboratory routinely monitors process chemistry, we visually inspect parts before and after anodising and for specification work, eddy current gauges are used to measure the film thickness non-destructively. The accuracy and precision of measurements taken with these gauges are sensitive to material composition and surface finish.

We carry out periodic corrosion testing, coating weight and abrasion resistance testing on standard panels.

If you require batch or part specific tests these should be specified in the contract or on the drawing or order.

Applications & Industries

Sulphuric anodised aluminium is used in industries such as:

  • Aerospace
  • Firefighting
  • Military & Defence
  • Packaging
  • Automotive & Motorsport

And for purposes such as:

  • Vehicles incl electric cars and batteries
  • Household and industrial appliances
  • Food equipment
  • Furniture
  • Electronics
  • Acoustics
  • Scientific instruments

Similar Processes

How We Can Help

We provide anodising services for the most challenging components and applications. We often take on the projects that other anodisers are unwilling or unable to do. We have extensive experience with dual-finishing, selective treatments, masking, creative jigging and multi-process finishing of complicated parts to achieve exceptional results. Get in touch with us for your next tricky project.

We provide a fast, high-quality anodising service that you can rely on. Customers from all over the UK and beyond choose us for our attention to detail and superior standards. Our quality system is designed to spot issues before they happen and save you time and money. We have an on-site laboratory for continual monitoring of tank chemicals, we do a full visual inspection of parts before and after processing, and we check thickness using eddy current gauges.

Choose a service that gets it right first time with fast turnaround and friendly service to match - get in touch with us today.