DIY Home Aluminum Anodizing


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  • DIY Home aluminum Anodizing for a Hobby

    DIY Information on home anodising (or anodizing!) aluminium (or aluminum!) using simple methods and inexpensive dyes.

    Disclaimer - None of the following is garrenteed to be strictly accurate. However it is garranteed to be extremely harmful to your eyes, fingers and other extremities if you don't take care with chemicals. Take care and don't blame me if it all goes badly wrong.

    Spelling - anodise or anodize - I am British. Many people are American. I spell in British English. Aluminium Anodising. Other countries spell this Aluminum Anodizing. I am going to stick to Aluminium Anodising. I do wonder if Google knows the difference. I also say Sulphuric, not Sulfuric. However, I might spell it another way just for variety!

    Anodizing Aluminum - Introduction.

    Aluminium alloys are a good choice of metal for home machining. I normally use aluminium on my mini-lathe to make telescope parts, camera adapters and other useful bits and pieces. There is an unfortunate drawback to using aluminium in this way. The main advantage and disadvantage of aluminium is its relative softness to other metals such as steel. This soft nature makes it much easier to machine on a mini-lathe than steel, but, once you have completed your part, it is very susceptible to small dents and surface scratches.

    Chemically speaking, aluminium is an extremely reactive metal. We are familiar with the action of the environment on iron. It oxidises quite readily to produce iron oxide - or rust as it's more commonly known. Aluminium is more reactive than iron, and, as such, will rust more readily. However, with aluminium a rough layer of aluminium oxide forms which strongly inhibits further oxidation. This is why aluminium is known for its resilience in corrosive environments - eg car radiators or boats. After a period of time the aluminium "rusts" - slowly producing a white powdery coat.

    Thankfully for the aluminum industry there is a technique which overcomes the inherent softness of the metal and protects against further oxidation. Using chemical processes it is possible to build a carefully controlled layer of aluminium hydroxide on the surface of the metal which is extremely hard - much harder and more durable than the rough natural oxidised layer that normally forms. The process involves suspending the aluminium in and acid bath and passing an electric current through the it. This is known as anodizing - so called because the aluminium part forms the anode in the electrolysis bath.

    The other advantage of anodizing aluminium is the potential of coloured anodizing dye. Coloured dye seeps into the microscopic pores of the anodized layer and colours it. The layer is then sealed and the colour appears as part of the aluminium metal itself. This can be used to great artistic effect, producing aluminium parts with strikingly tasteless colours to adorn your motor bike or, more topically, telescope. With optical applications, black is the most popular anodizing colour to reduce internal reflections. Typically of course, black is supposed to be one of the most difficult colours to achieve and commercial black anodizing dye fetches the highest price.

    Anodizing aluminium (or indeed anodizing aluminum) is a fairly simple process, and providing you can lay your hands on the correct chemicals (ie sulfuric acid) it is fairly straightforward to do simple diy anodizing aluminium in the home. I would limit yourself to anodizing aluminium in fairly small amounts - if you want to anodize a large object you need a lot of electrical power and a lot of acid, so if you want to do an entire bike frame in one go, I suggest you contact an aluminium anodizing company.


    Contact me on tomh at tomh@tomhow.me.uk

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