How to remove anodization February 24, 2015, 08:58:57 am Materials needed:plastic bucket big enough to put your part indrain cleaner from the hardware store (the lye variety)warm waterterry cloth towels.anodized aluminum part to be stripped "parts washer" gloves (elbow length rubber gloves)safety glassesrespirator (optional, I wouldn't recommend doing this inside anyway but even outdoors you need to steer clear of the vapors!)Bottle of vinegarJust a preface, I needed to clean up a very unusually sized wheel (no replacement available) and make it shine. From the factory it was gold anodized and then someone had painted over that flat black. I'll save the pictures of paint stripping using hardware store gel paint stripper but suffice to say, that step took some time but not much science. The anodization removal took some science but not much time...Anodization is the process of oxidizing a very thick layer of the surface of aluminum and then coloring that layer before "closing the pores". Believe it or not, those brilliant colors are ordinary food coloring trapped inside a thick layer of aluminum oxide on the surface of the aluminum. They do this by dipping the part to be anodized into a chemical bath and electrically charging it. The chemicals in the bath oxidize the surface in a uniform manner (much thicker, also than normal weathering on aluminum) and leave the "pores" of the metal surface open. While the part is still hot, they dip the part into a food coloring solution for a predetermined amount of time and then "close the pores" by rinsing in cold water. In order to remove anodization, you have to remove that oxidized layer. A "normal" oxidized layer on aluminum is .0005"-.001" thick or about 1/8-1/4 of the thickness of a human hair. This can be "cut" off with rouge or buffing compound. Anodization, depending on how long it's left in the solution, can be .010" thick and you would spend AGES in there with sand paper (not to mention the deep gouges left after 80 grit sand paper) and even then, you wouldn't be able to get down inside every crevice....The best option is chemical stripping. Ace hardware to the rescue!!!!This is a product sold as drain cleaner, it's granulated 100% sodium hydroxide (an EXTREME base also known as lye). It is extremely dangerous. It will permanently blind you if you get it into your eyes, dissolves your skin by turning it into soap, and will hydrolize your lung tissue so DO NOT BREATH THE VAPORS. This is NOT stuff to play around with especially in the concentrations we're going to be "playing" with. This is the botom half of a shop vac with about 3 gallons of WARM water poured into it. DO NOT POUR BOILING HOT WATER IN THE BUCKET, YOU WILL REGRET IT LATER. Warm water gets the reaction going and allows the sodium hydroxide to dissolve. It also makes it much nicer on your hands if it happens to be cold out (note: see snow on the ground behind bucket )Now, I specifically said warm water in the bucket because sodium hydroxide into water is an exothermic reaction. As it dissolves it will heat the water chemically. If you put water in the bucket that's 180°F it will be boiling before you can get the solution concentration we're looking for. Warm water only, not hot, warm!You are looking for a strong basic solution on this, I went with 2 tablespoons per gallon of water. That was overkill and probably too strong, you could go with less. The reaction speed and danger level drops as the content of lye drops but it will take longer to do and considering it was about 20°F outside while I was doing this I threw the pedal to the metal! Put on your large rubber gloves, safety glasses, and respirator now.Pour the granulated lye into the water SLOWLY allowing it to drop in a little at a time. If it falls to the bottom and doesn't dissolve use a plastic (note: no wood or natural fibers, it will just eat them) spoon or something similar to stir slowly. You will see the lye dissolve and the water will get "cloudy" for a minute. Slowly add lye to the water as you stir until it's all dissolved.Lower item to be stripped into the solution (no splashes, this crap eats everything) and stir gently. The reaction works quite well if you let it sit there too and you can watch the bubbles come off of the metal as the reaction takes place but the areas where the bubbles "stick" to the metal will be all cheetah spotted. This isn't any kind of an issue especially at the beginning but the final dip into the liquid you will definitely want to make sure you stir the liquid and wipe the metal to reduce the effort later in getting it shiny.