Anodize Aluminum Easily

We’ve all seen brightly-colored pieces of aluminum and can identify them as anodized. But what does that mean, exactly? A recent video from [Ariel Yahni] starring [Wawa] — a four-legged assistant — shows how to create pieces like this yourself. You can see [Wawa’s] new dog tag, below.

[Ariel] found a lot of how to information on using sulphuric acid, but that’s dangerous stuff. One web page we covered years ago, though, discussed a safer chemistry. The process requires lye and a common pool chemical used to decrease pH. Sodium hydroxide isn’t super safe, but it is much less problem to buy, store, and use than battery acid.

Aluminum naturally forms an oxide layer on its surface when exposed to air. Anodizing in an electrolytic cell creates a thicker oxide layer that makes the part more resistant to corrosion and wear. It also presents a porous surface that will easily take dye, leading to the bright colors you often see on anodized pieces.

In this process, the lye is used to strip the surface. Then it’s on to anodization in a solution of sodium bisulfate, with a repurposed 12 V, 2 A power supply putting a bit of current through the piece. The trick is to realize this is anodization, not cathodization. Chemically, this is the sodium salt of sulphuric acid, and you can dispose of it safely after neutralizing it with baking soda. Rit dye can provide coloring.

Overall, this is a good trick to anodize with nothing more than a trip to your local home improvement store. And [Wawa] got a stylish dog tag out of it. Win, win.

If you have some titanium you want to anodize, we got you covered.

23 thoughts on “Anodize Aluminum Easily

  1. >>Sodium hydroxide isn’t super safe, but it is much less problem to buy, store, and use than battery acid.

    I would rather handle concentrated sulfuric acid than deal with strong bases.
    NaOH is at least as dangerous as sulfuric acid and just as difficult/ easy to store. If you can find premixed liquid solutions of lye that takes some of the danger out but I’d wager most people get their lye as powder. Plenty of opportunity to get a face full of fine lye powder or to have it spatter while dissolving into water. Compounded by strong bases not causing as much pain compared to acids as they burn you, you might not notice a splash until it’s done some damage.

    1. Absolutely! And, because the lye reacts with the fat in your skin, turning into soap, it is nearly impossible to wash out without severe damage. In your eyes? You didn’t need them anyway. Give me good honest acid anytime, at least I know when it is on me.

    2. Battery acid is not concentrated sulphuric acid. It is dilute sulphuric acid at about 37%. When used for the anodizing process, you further reduce the concentration down to around 3-5%. Battery acid is not hard to find. Practically every auto parts store in the US sells it, even walmart. Also, the sodium hydroxide solution does not need to be strong. It can be quite dilute to the point that it is safe and still be effective at etching/cleaning the surface. The warmer it is, the lower the concentration can be. Also, you dont want to etch in lye for long, if at all (depending on the alloy), unless you want a cloudy dull surface like in the video, which does not look good.

      1. I’m not aure if they’re referencing actual acid meant to refill batteries or the fact that dilute sulfuric acid is battery acid. Concentrated sulfuric acid is readily available if you know where to look, so it’s entirely possible they could be talking about 96-98% technical grades.
        Whereas sodium hydroxide is most commonly available as a dry solid for dyeing laundry, soap making, or drain clearing. My concern was more over the dry chemical than dilute solutions. As you say, dilute solutions of either are fairly safe ( as far as acids & bases go) but diluting them is something you need to pay attention doing.

    3. Based on my own personal experiences I would have to disagree with you about the pain level of burns from sodium hydroxide and other strong bases. I would say that they are about equal in pain level and how quickly one feels that pain.
      That being said, I agree with you completely about being more comfortable working with acidic vs. basic chemicals.

      1. Fortunately I’ve managed to avoid chemical burns so I only have the ‘common wisdom’ to base my relative pain on. Dealing with pure, dry bases seems like an easy thing to hurt yourself doing compared to liquids of either.

    4. here NaOH is usually ~2mm pellets sold as drain cleaner, back in the day when developing PCBs at home was a thing I’ve often gotten it on my fingers with no other effect than they feel “slippery” until you wash them. I wouldn’t recommend it but it doesn’t seem that dangerous

    5. I’d rather clean up the mess from spilling NaOH pellets on the floor or bench (dustpan and brush) than the mess from spilling conc sulfuric, which gets into and under everything.

  2. I came up with this process and it was posted here in October of 2011. Since then I have recommended professional dye and have 500 comments on my site which is open source but I ask that my site to be recognized for the process. The procedure is easy and works well. Best to all who give it a try.

    1. Ken – any sage wisdom about how to keep the anodizing from abrading away?


      Here’s the original link referred to in the 2011 article:

      And the 2011 article itself:

  3. I just had a medical prototype I designed and machined delivered in final stage to me and I and my business partner had production parts Hard anodized (type 3). This annodizing is called type 2, its mainly for looks and color change.

    You can get clear anodized, but its still a light straw gold color.

    If you have anything you want seriously wear resistant, you need massive current for type 3 hard coat annodized. If you pay to have it done it’s often not much more expensive. If you just need color, this totally works, I’ve home annodized too. Good stuff!

    1. Almost forgot- there is a special class of anodizing called architectural anodizing that is fade-resistant in UV light often used for stuff outdoors, which uses metal particle dyes instead of inks for color. Very few places in the u.s. do this though.

      You can also get something professionally anodized with Teflon impregnation, if you want it to be a color and slick but wear resistant.

  4. Perhaps a safer alternative is oxalic acid anodizing. I tried it once—-just anodized, no dye—-and it gave a decent finish. Oxalic acid is poisonous, but it’s a weak acid that requires only normal lab safety: nitrile gloves and eye protection from splash. Got some solution on your arm? Wash it off, no huhu, it won’t burn and smoke the way sulfuric does.

  5. You can clean aluminium prior to anodizing safely without sodium hydroxide (lye). You can substitute sodium bicarbonate (sodium hydrogen carbonate, NaHCO3, baking soda) or disodium carbonate (Naa2CO3 washing soda). If you don’t believe me, try it with some aluminium cooking foil first. First, place your aluminium foil in a pot with water on the stove and add some baking soda or washing soda and heat. Over 50 deg. C, baking soda decomposes to washing soda. As the temperature increases, you’ll start to see the aluminium foil dissolve, with bubbles of hydrogen being emitted. That’s because the protective oxide/hydroxide fim on the aluminium is disrupted by the carbonate, allowing the naked aluminium metal to react with the water, genearting hydrogen and forming aluminium hydroxide. Now try it with the piece of aluminium you want to anodize. You should be able to scrub off any loose hydroxide film on the surface. BTW, you can clean silver by placing in water with aluminium foil and baking soda and heating until all the aluminium foil dissolves.

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