Anodizing small aluminum parts
With a lot of projects coming out of my shop made of aluminum, I needed some way to finish my work. The only really good way to finish aluminum is through anodizing. This process results in a coating that protects against oxidation, reduces scratches, and looks good. It's actually a fairly simple process but it does require the use of some potentially dangerous chemicals.

I assume no responsibility for any use of the information on this page. I'll tell you what I've done and what's worked for me. This process could be dangerous and I'll assume no liability for your actions.

Having covered myself that way...It's a pretty easy process that requires little special equipment or materials. The results have been very satisfying for me, producing finishes that are much nicer than just bare aluminum. I learned the process from the internet, especially Chris Heapy's excellent page on anodizing.
Anodizing involves the imersion of the part in an electrolyte solution while a current is passed through the solution and the part. As oxygen is formed on the anode (the positive terminal which is the part) it reacts with the part to form a thin layer of aluminum oxide on the surface. After anodizing the part can be soaked in dye which penetrates the still porous (relatively) layer of aluminum oxide. The final step is sealing the oxide layer by imersion in boiling water.

My whole set up is outside on a folding table (actually a portable shooting bench I made years ago and use for everything except shooting). The two plastic tanks on the table are 5 qt. food storage containers from the supermarket. They were really cheap. They are a good size for small parts. And they have tight fitting lids. The one on the right holds a weak lye solution (2 tsp./gal) for etching the parts before anodizing. The tank on the left is the anodizing tank. It is filled with dilute sulfuric acid (1:3 battery acid and distilled water). After etching, the parts are rinsed in distilled water and moved to the anodizing tank. Power is supplied by a battery charger. The current runs from 2 to 10 amps depending on the number of parts (more surface area = more current). The anodizing takes about 1.5 to 2 hours. The parts are rinsed again and dyed if wished. I started only dyeing parts black using Nigrosin stain (1 tsp/qt.). Soaking in the dye for at least 1/2 hr. seemed to produce the best results. The pan on the ground at the right contains the stain. Most authorities advised heating the dye to 120-160 degrees F. I haven't been heating the stain, just leaving it outside or in the garage (where it's over 100 degrees every afternoon).

Lately I've been using dyes from Caswell plating and just following their directions. A bit more expensive than the generic Nigrosin, but with better results and lots of different colors.

When the parts come out of the stain, I rinse them again, then immerse them in boiling water for at least 30 min.

At left is the anodizing underway. Ouside is a good place for this process. It gives off a fair amount of noxious fumes (sulfuric acid fumes).

My comments - The parts need to be completely clean to start with. I've been washing them carefully with dish soap and rinsing under the tap and then with distilled water.

Be very careful not to let the parts dry once the process is begun. Working outside where it's very hot and very dry it's easy for the parts to dry partially when moving between etching/anodizing, anodizing/dyeing, etc. If the parts dry at all it produces uneven patches in the finish.
If you've ever thought about anodizing things yourself, I recommend it. I got set up in one afternoon (for a very small investment) and was getting good results by the second batch. Have fun, but be careful.

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Cheers, Kelly

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visitors since 15 September 2001