Q&A for How to Anodize Aluminum

Lye is Sodium Hydroxide (NaOH). You can find it in grocery stores in drain cleaner, clog removal chemicals, or the plumbing section.

No, you do not add dye to the acid/water solution at all. The dye bath comes after the part is rinsed in clean water.

The cathodes can be lead (element Pb), although people successfully use aluminum rods or plates as well.

To be clear, the leads do not have to be made of lead (element Pb). This is just the name given to a wire that carries electric current (in DC circuits that is). Any wire that carries electricity should suffice, in this case they use aluminum leads.

Yes, the surface is non-conductive. You can imagine it as an electrical conductor (aluminum), covered by an insulator (anodized layer).

Yes. The acid (battery acid) you get at the auto parts store is 37 percent sulfuric acid. Mixing 50/50 with demineralized water gives you approximately the right concentration (should be between 16.5 and 22.5 percent).

Yes, you can, but the current he lists here is too low to be hard-coat, so it is not the same as buying one anodized. To hard-coat, you need to do at 32 F and use a regulated power supply to slowly ramp your current up to 24 - 30 A/sqft. The instructions here are type II anodizing, and if you are looking for Type III, you will be disappointed with the durability.

No, you can use anything aluminum you like, as long as the aluminum touches the object you want to anodize and your positive lead. I bought wire from Home Depot so it's not hard to find and it's the easiest way to suspend the object you want to anodize.

No. You want to keep the acid bath as cool as possible during the process (50-70 degrees F max), while the dye bath needs to be considerably warmer (~120 degrees F). Use separate tubs.

The aluminum part decreases its overall dimensions slightly but is substituted by the anodized layer, so final dimensions remain almost the same.

You can't. Unless the aluminum is completely alone, there's a really good chance the other metals are just going to contaminate the solution. Try to get the aluminum as far away as possible from any metal other than aluminum or lead.

No, hard anodize needs to be done at a low temperature, somewhere in the 30's should be good.

Most likely not. Because the aluminum has a plastic coat, the powder coat would first have to be removed before attempting the anodizing process.

The 6000 series and 5000 series anodize best and take the dye most consistently. The 2000 series and 7000 series will also anodize, but it is a bit harder to get it right with them. Honestly, though, any aluminum will anodize.

Yes, and to the extent that the wire is in the acid solution, this will happen anyway. However, once it is anodized, it becomes a poor conductor because of the insulating nature of the anodized surface. For this reason, using a fresh wire each time will yield more consistent results.

If you keep the temperatures low, you can dip the majority in molten wax and then anodize the exposed parts. After that, clean up and cover the other parts in the same way and do the next color.

Use black dye after the anodizing and rinsing stages.

This is considered type II anodizing considering the quality of the aluminum.

The same way you do here. The methods differ for different alloys, not for different sizes.

You can, but the whole point of anodizing is to give your part a nice color that won't be easily scratched off.

You patina copper, you can't anodize it.

Yes. After the metal comes out of the acid bath after anodization, the oxide layer is still porous and will take up the dye nicely, and the pores will be sealed after boiling in water for some time.

You need to dispose of them safely; the acid is the most difficult part to dispose of. Do not throw it down the drain. Instead, mix it with lots of baking soda (until you don't see any bubbles) and then mix that with water. Finally, pour the mixture down the sink! The dyes also need to be disposed of carefully, but you do not need to use baking soda. Just dilute them with lots of water and pour them down the drain.

You don't add it to the anodizing bath. You mix it separately and heat it to about 140F, then remove your part from the anodizing bath, rinse it, desmut if needed, rinse again, then put it in the dye bath.

5 grams per every cup of distilled water, or 3 tablespoons per gallon of distilled water.

Boiling is the easiest way. Nickel acetate works better overall for durability, but honestly isn't worth the hassle or money unless you are doing type III anodizing.

You shouldn't wait between anodizing and dyeing, as the pores the anodizing process opened will close before the dye would have the chance to go in.

Sanding only changes the surface of the material, but does NOT remove the unseen oils, like from your hands, so it needs to soak. If you want a dull surface, then sanding will do that. The lye will get into the pores and small places and remove any contamination.

Almost all colors that can be used for cotton or silk or wool can be used for this. Make sure that it is a dye soluble in water and immerse the anodized piece into the dye solution for some time (mix the solution every 1-2 minutes and shake well), and when you think sufficient color has been taken up by the piece, seal the pores with the dye inside by boiling it in water for some time.

Aluminum oxide. The sulfuric acid forms hydrogen gas at the cathode and oxygen gas at the anode. The oxygen gas immediately interacts with the submerged aluminum surfaces and forms a buildup of amorphous aluminum oxide.