How to: Anodize aluminum

I absolutely love this this new video from Engineer Guy Bill Hammack. Why? Because Hammack managed to make me intensely interested in something I'd previously never really thought twice about—the anodized aluminum coatings that cover—most famously—Apple products.

I sat down to watch this video expecting to be bored. By the end, I was captivated. What more can you ask for in an explainer?

Video Link


    1. It must be old age, but anodized aluminum doesn’t make me think of Apple, but drinking glasses from the 50s.

      1.  Invented in 1923 by British Defense to protect sea planes. Scuze me. iPlanes. Because Apple invented everything.

      2. Yeah, I’ve been at least slightly interested in anodising since I saw those as a little kid. Became somewhat more interested in it when I got into tweaking my BMX in the 80s.

        Back in the day, I used to pity the guys who had those crappy chromed steel rims on their bikes that had a flaky coat of clear yellow laquer clearly intended to ape gold anodising…

        It’s such a cool means of bling. Coloured metal, it’s almost scifi. I love how it puts a really tough surface on ally, which is a wonderful material, only a bit soft.

      3.  I fondly remember those glasses. I often consider buying a set of the newer version, but hesitate to do so since it’ll outlast me by decades. I like the look of annodized metal.

        1. My aunt and uncle had them. I seem to remember thinking that they were naff.

  1. I love anodized aluminum.

    Over the past few months I’ve been spending weekend time studying jewelry making with a very accomplished craftsman (he’s been doing it for 40 years, me a few months), and last weekend we were looking though some pieces in a book he had on folded metalcraft. He was pretty dismissive of it for all sorts of reasonable reasons, so I guess my love of it is a bit lowbrow, liking it for the same reason that you love colored cellophane as a kid: it’s bright and colorful.

    But I still love it, and I hope that part of the kid in me never dies!

    1. There was a craze for anodized titanium jewellery a few years (or hey, might have been decades?) ago. The colours are beautiful.

      I gather it is not an easy metal to work with. Perhaps you might like to give it a try!

      1. In niobium and (I think) titanium a particular color can be achieved by controlling the film thickness to reinforce a desired light wavelength.  THAT is cool!

  2. I like this guy. He’s like the new Mr Wizard to me. So friendly and and smart and yet manages to teach effortlessly. 

  3. When I think anodized aluminum, my thoughts jump right to carabiners, not Apple gear. Of course, I neither climb nor play with Apple toys, so who knows how universal my experience is.

  4. What has this remotely to do with Apple?  Anodizing was well understood and in use long before Jobs and Wozniak were born.  I’m not a big complainer about the universe’s most haloed consumer products company but I’m getting tired of mundane things being discovered and wondered over because they’re employed by Apple.  It’s surface metallurgy.  Get over it.
    Spoiler: the color is a dye.
    You’re welcome.

    1. Dude, the wonderment has nothing to do with Apple. The wonderment has to do with there being an incredibly cool process behind something I never thought twice about before. 

      Apple is only mentioned because it brings to mind pretty quickly what the heck I’m talking about when I talk about anodized aluminum. 

  5. This is essential knowledge for fabricating the to-die-for sub-$100 sturdy NASA-aesthetic day pack.

  6.  Engineerguy or not,  Aluminum Oxide is not rust.  “Rust” is specifically Iron Oxide.  Even naturally occurring Aluminum Oxide (not just under controlled settings) protects the metal underneath, “rust” or iron oxide continues to oxidize until the metal is completely corroded.

    1. My understanding is that what you say is true for steel and malleable iron, but with cast iron, the iron oxide coating works in a similar way to anodizing and it protects the underlying metal.  Perhaps not as well as anodizing, but it significantly slows the oxidation process and the cast piece will not ‘rust away’ easily.

  7. I’ve had anodized aluminum tumblers since I was a kid; my mom grew up with them, and they were durable enough that she was able to bring them with her through college, the first couple years of her marriage, and my clumsy-ass childhood. 
    It’s cool to finally learn how they make the magic happen. Or, rather how they make the material that I put in the freezer when I was five, which I then poured Kool-Aid in, and handed to my sister and laughed when her mouth got stuck. That was the real magic. And then she spit the Kool-Aid at me. Best dual grounding ever.

  8. Back in the 80’s and 90’s, aftermarket bike parts came in all manner of anodized beauty. I’m still rolling with my anodized-red Avid Tri-Align II brakes on my bike.

    1.  BMX parts were often anodized aluminum. And if we got tired of the color, we used to strip them down to the raw aluminum using “easy-off” oven cleaner. I don’t recommend this for electronics.

  9. I think Tektronix had the best idea. They would anodize a thin sheet of aluminum, but not seal it. They then printed front panel graphics on the panels and sealed them. Made the best looking and durable front panels in the industry.

    1. Another neat way of putting durable markings on anodising is to etch through it, often with a laser.

      I’m still waiting to see a part somebody’s anodised again in a different colour rather than leaving the etched metal bare…

  10. I absolutely hate this this new video from Engineer Guy Bill Hammack…..and all his other videos I have seen.  He is the  John H. Davis of engineering entertainment.

    1. That’s a bit strong, but I agree he definitely over-simplifies.

      There’s no call to go using the term ‘rust’ with anything other than ferrous metals. Not cool.

      1.  Rust is just a special case of oxidization.  Most people will understand “rust” but will need “oxidization” explained to them.  For a simple, popular educational video it makes sense, even if it’s not technically correct.

  11. Used to play  A LOT of paintball. Most of the guns were aluminum and they got pretty fancy with colors, designs, and fades. I still have a few projects that I need to get anodized – just never got around to it.

  12. Couple of more interesting facts about anodized aluminium.

    1. The number of colors is essentially infinite, to get brighter colors you can “brite-dip” the part prior to anodizing, this is a form of chemical polishing. The “brite-dip” process is particularly harsh, the chemical polishing solution is made up of various acids and heated to near the boiling point of water. The solution is harsh enough to etch 316 stainless steel.

    2. While hot water sealing does seal in the dye used to color the material, most dyes used in anodizing are organic. As a result they will fade over time. Thus, parts anodized black, blue, or red will fade in direct sunlight after a few years. The one color that won’t fade is gold. The gold dye is inorganic and thus doesn’t fade. A gold anodized shower door will look great for over twenty years.

    3. The anodized aluminium coating is a dielectric (it will not conduct electricity), some companies use hard anodized (a thicker denser anodic coating up to .002″) aluminum shims as insulators. Yes, that is right they use highly conductive aluminum parts as insulators.

    4. Anodic coatings are tough but not indestructible. The hard anodized pots and pans from the makers of Calphalon should be hand washed. The combination of hard water and silght alkali nature of most automatic dishwasher detergents will slowly break down the coating over time. Strong acids and bases will damage anodized parts over time. Sometimes quite quickly.

    5. If you wish to remove anodize (for example, you wish to polish your aluminum car parts) you first need to remove the anodize. The anodic coating is very durable, polishing it off is time consuming and frustrating. So you can remove the anodize with a little Easy-Off Oven Cleaner. The harsh caustic solution in Easy Off will remove the anodize in as little as 10 minutes.

    6. While anodize is damaged by strong bases and acids, it is impervious to most petrochemicals. Acetone, lacquer thinner, brake cleaner, won’t harm anodized parts. Some engine degreasers contain caustic chemicals and thus should be avoided.

    7. Finally, to make your anodized parts look really good, clean with a mild soap and water. You can wax anodized parts with a non-abrasive carnauba car wax for a little more shine and to prevent water spotting. Finally to make it really look good wipe down any anodized parts with a little WD-40, it will remove any water spots and make the part really look it’s best.


    1. I did a brief stint anodising yacht masts. We didn’t use hot water to seal the parts, we dunked the gear in some green stuff I’ve forgotten the name of.

      No idea whether it was a superior process, but keeping a 20m long bath near boiling wouldn’t be cheap…

    2.  Another way to remove anodized coatings is to let your babysitting mother in law wash your pots and pans.  Comet and steel wool instead of a sponge and Polmolive will take the coating right off.  And look, now the pot is shiny!

    1. Do you have a source for that? It was my understanding that all the unibody MacBooks were anodized aluminum.

  13. Both BoingBoing and Bill Hammack lost some respect with me today. Paul Jenkins above gets it. It’s not “aluminum” (unless you’re George Dubya Bush). It is aluminium. Nevertheless, the process is amazing.

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