Aluminum Anodizing Tips

Aluminum Anodizing, Anodizing Dyes, Tips and Tricks!
We have better perfected the anodize process and are using better quality dyes from US Specialty. For dyes and further information please visit our other website:

We are currently not doing outside anodizing since we don't have production capabilities and our anodizing time is taken up by other processes. Anodizing aluminum is a complicated process and the tank here is set up for smaller hardware runs.

The Anodizing Process:
    Anodizing aluminum can be difficult. I will start a blog here about the process because many people try to anodize but run into problems. There is little real information on the internet as well. Many sites give amperage formulas and the like but can be difficult to follow. Over time I have better perfected the process and am always learning as well.

    This type of anodize is done in a sulfuric acid bath, battery acid and water. Around 20% of acid to water should be fine. It's easier to start with a thinner mix and add more acid rather than take it away. This step is really important as it will have an effect on the current and it's density. In my experience the tank also needs a bit of aluminum, after a few runs the tank will break in and anodize will become more steady in it's formation.

    A good variable power supply is needed. I've hear of a car charger being used but have never tried it. I use a variable supply with 3 amps maximum. This is enough to anodize 2 or 3 160mm rotors at a time. I usually set the voltage to be constant around 14.5v and let stay in the tank for about 80 minutes. Sometimes I will leave in a bit longer because some colors need a bit more anodize.

    The metal things going into the tank are anodes. They should be much greater in surface size than the parts you are anodizing. Titanium is the best solution. I use old titanium rotors and titanium wire to connect to the tank. They need to be cleaned occasionally but will last for years.

     The dyes need to be heated to 140 degrees (generally). PH needs to be low as well. Pet stores sell electronic testers and ph down which does the job. Some colors like reds and purples wont take well unless the ph is lower. US Specialty dyes will boost the ph and this in combination with water will require careful checking.

Time in tank
    The parts will need to be in the tank for as long as it needs to anodize. Start with scrap and learn before doing expensive parts. The parts should have a grayish look when done. Wash very well after the acid before dye. Time can usually cut down by increasing voltage but can form a poor coating. Temperatures should be around 68 degrees. 

    Boiling water alone will work. If the dye flushes out at this point the anodize is no good. A hard boil or steam for 30 minutes will lock the dye in.  I use nickel acetate seal from US Specialty. The nickel molecule gets trapped in the pores and requires less heat and shorter time to seal properly.
    Boiling will make a tougher surface. The nickel will have a bit nicer look and a bit more shine as an end result. For me it make sense to use a good sealant.

End Result
    Your finished job should look nice. If it looks nice its basically ok. You should have deep color and wont be able to wash the color off with bleach (Bleach will strip the dye out of parts not sealed properly). Patience and experience will really help.

Problem Solving
1. Pitting parts: Acid too strong also new tank without aluminum seeding.
2. Burnt parts: voltage too high
3. Wont take full color: Not fully anodized. Needs more time or more power.
4. Parts loose color in seal: Temperature of tank too high, Anodizing pores too large. Too low voltage.
5. Parts loose color over time: Bad sealing
6. Some dyes take color and some don't: Some colors need different temperatures in the acid bath. Play with the temps and try different colors to find the correct tank temperatures. Dye PH wrong.

If you have any tips to add or questions please leave a comment.

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