A short film sharing what I’ve learnt about low current density anodising of aluminium from my limited experience in the home workshop. This isnt meant to be the right way, or even a good way, its just the way I do it.

The technique provides a measure of improved durability / corrosion resistance to parts, as well as changing the aesthetic.

I didn’t mention that the chemical baths can be reused over and over, so no need to remix for every job.

Useful links and further reading:

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Changes to the rules surrounding the supply and possession of sulphuric acid in the UK during 2018:

www.gov.uk/government/publications/licensing-for-home-users-of-explosives-precursors/licensing-for-home-users-of-poisons-and-explosive-precursors

and

assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/694030/FAQs_general_public_v4_-_Mar_2018.pdf

For those speculating about the reason for the withdrawal of concentrated sulphuric acid products from general sale in the UK, this article might give food for thought:

www.bbc.co.uk/bbcthree/article/5d38c003-c54a-4513-a369-f9eae0d52f91

youtu.be/9pZIl2EwlvY

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The use of sodium bisulphate in place of sulphuric acid:

www.observationsblog.com/sciencetechnologyexperiments/anodizing-and-dying-aluminum-without-battery-acid

www.youtube.com/watch?v=7jFN3l_mrKk

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A 15% acid solution seems to be what many people aim for. There’s pros and cons to higher and lower concentrations but they’re beyond the scope of my little setup. finish.com has a wealth of information:

www.finishing.com/11/30.shtml

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Some 720 rule calculators.

The one featured is by by ‘kreutz’, mainly as I can use metric sizes with it. 1 mil is an optimistic coating thickness for sulphuric anodising -thicker coatings require hard anodising which is beyond the scope of this film.

chemeon.com/p/calculator/

www.ndhsubmersiblescience.com/ano/720rule.html

www.hobby-machinist.com/threads/diy-anodizing-at-home-720-rule-calculator-for-low-current-anodizing-method.6775/

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POST UPLOAD UPDATE:

Thanks for all the comments and feedback :-)

Ive read them all, but I’ve not the time to respond individually. There’s some interesting ideas I can play with next time I get the anodising stuff out.

Some (mainly US) viewers seem annoyed that the UK government would take steps to try to ensure the safety of their citizens by making it more difficult to obtain something that (a small minority of) the general public has demonstrated theyre too stupid to have free access to. It’s a minor inconvenience to me, and good reason to re-visit bisulphate method. I dare say the persistent shopper will still be able to obtain it, but I wanted viewers to be aware of which side of the law both buyer and seller will be on if the relevant paperwork is not available. Perhaps there’s a market for selling pre-diluted 14.9% H2SO4 to the home anodiser?

As for the availability of lead, I should probably have said “small quantities of clean lead sheet are surprisingly hard to get hold of”. Larger fishing weights are still made from lead, as are old tyre weights (new ones are other metals) and these could be fashioned into sheets if I had the inclination. Lead flashing is available at every DIY store, but I can’t justify the cost of a 3 metre roll for the sake of a couple of small pieces. Ive since obtained some from a friendly roofer ;-)

I’m not a chemist, but I believe having too little acid to mix to the original calculation left me with a solution of around 14.5%. Given my uncalibrated scales and general ball park approach, I didn’t think it was worth the re-calculation / re-weighing / re-filming for a couple of percent difference. With concentration, time, temperature, current density and material all playing a part (and being beyond the scope of my simple setup) I just wanted to get on with it. Note: You can’t just divide the weight of acid by the weight of water to get a percentage, it needs to be the weight of acid by the weight of solution (i.e. acid plus water).

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