DIY Home Aluminum Anodizing

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  • First Experiments DIY Anodizing Aluminium

    Ever since I have made things out of aluminium, I have had a desire to anodize them. Recently I finally got around to pursuing this idea - this was all started by finding a supply of the required acid. After that it was all surpassingly simple.

    Instead of plunging into an accurate description of my refined anodizing technique, I am going to run through initial experimental trial.

    As mentioned above, I have wanted to try anodizing for some time, and have read quite a few websites on the subject. However, the stumbling block was getting hold of enough sulphuric acid (H2SO4). By "enough" I mean at least 2 or 3 litres of 20% sulphuric acid solution. Two or three gallons would be better.

    Now, sulphuric acid is battery acid - so potentially you could buy lots of batteries and tip it all out - but that acid may well be contaminated. This also sounds like an expensive approach. My local automotive shop (Halfords) said they are not allowed to sell the stuff. So I was a bit stuck. Then I discovered an online shp which seemed to sell all manner of exciting chemicals mailorder. Then next day 500ml of 98% sulphuric acid arrived. Cool!

    November 2007: Please note the shop no longer exists. It is very difficult to find anybody selling the chemicals these days. It might be worth talking to these guys for advise. Also, some places sell battery acid which should work - I think battery acid needs to be cut 50/50 with water to be the right strength for anodizing. for example...

    Here I ought to mention how nasty Sulphuric Acid is. Wear all the required protective clothing etc etc and make sure there is a nice big bucket of cold water nearby which has a load of bicarbonate of soda mixed up in it. If you suspect anything of having acid on it, dip it in the bucket and it will fizz. This includes you hands. Wash down the work areas afterwards with the bicarb solution. occasionally wiping some over your face and other exposed skin won't hurt either. When the dilute solution gets on you or your clothes, you'll not notice straight away.. do be careful. The acid bath gives off all sorts of nasty gases as well, and you should really have a lid, or special fume absorbing balls floating in the acid bath. I didn't quite go this far, but make sure the work area is extremely well ventilated and don't breath near the tank.

    The first thing we tried was making up a small amount of acid solution in an ovenproof dish. To 300ml of water (pure, distilled, deionised water of the sort you might top up your car battery with) we added roughly 50ml of acid. Naturally this was all done with lots of gloves and eye protection. Remember - AAA - Always Add Acid. Whilst waiting for the solution to cool down a bit (adding acid creates heat) I had a dig around in the garage and found a roll of roofing lead. I was just able to lift it! I cut off a square with the sharp carving knife and bent it into an L shape and sat it in my acid bath to act as the cathode. Next I found a piece of scrap aluminium round bar and stood this in the acid bath so its bottom inch was under the acid. Using a PC power supply I connected 12 volts to the bath. The positive lead was fixed to the aluminium bar, and the negative lead attached to the lead cathode.

    When I turned on the power, lots of bubbles formed on the lead cathode, and a few bubbles formed on the aluminium anode. More bizarrely, a faint purple colour was seen around the aluminium. This is apparently due to manganese in the aluminium alloy.

    I left the whole thing to fizz for about 45 minutes. Then I removed the aluminium and washed it under the tap. I then mixed up some red food colouring with some water and stood the bar in this for about 15 minutes. It turned pink! Finally I boiled the part in water for half an hour to seal it. I ended up with a aluminium bar with a pink bottom!

    This was rather exciting! I promptly repeated the experiment with a bit of better finished aluminium - the result was amazing! I was very happy.

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