View Full Version : Finishing Aluminum (Anodizing?)

05-04-2006, 12:26 PM
I've got some projects that I'm going to weld up in aluminum, but I'm wondering if there is a way that I can finish the aluminum to help protect it and keep it from oxidizing. Is there any way that a person can anodize the stuff in a home shop? Or do I need to look at some other method of finishing the aluminum?


05-04-2006, 01:18 PM
Is there any way that a person can anodize the stuff in a home shop? Or do I need to look at some other method of finishing the aluminum?

Anodizing is easy, I do it at home no problem, excepting the occasional late spring snow storm.

There is tons of info about how to anodize online. Start here:


05-04-2006, 04:57 PM
Here is something that I noticed in the store today. I need to blacken some aluminum on a model and thought it might be worth a try. Has anybody tried it out?
product: Aluminum black

Maybe it will work for your project.


05-04-2006, 05:54 PM
I have used it. It works ok but the finish is far from durable. It isn't nearly as durable as cold blue on steel for instance.

05-05-2006, 01:19 AM

Looks like something that I'd love to try, but a lot more involved than I'd like to get into for the time being....especially for the amount of stuff that I'd want to do. Hopefully in time. I guess for the interim I'll make some inquiries about getting the few pieces I want done commercially.


05-05-2006, 01:40 AM
It isn't expensive but you do need to do it outside well away from any machinery because of the slight acid fumes. All you need is some battery acid, some containers like ice cream buckets and a battery charger, the dumb kind. I use clothing dye to color the parts. Parts with welds are harder to get an even coloring on because the filler is usually a different alloy than the work piece. Castings don't anodize well and for the 2000 and 7000 series there are a couple of extra steps required but still not expensive.

05-06-2006, 02:07 AM
Evan, rather than buying the kit, is there a site that lists the basic chemicals required? Looking at what this guy is saying, it seems that the most important thing is control of the temperatures.....is that right?


05-06-2006, 08:16 AM
The only chemicals required are battery acid and lye. Both are easily available. You also need a source of mineral free water, I use rain water. Temperature is somewhat important but accurate control is not necessary. The main consideration for most situations is to avoid getting the anodizing bath too hot. With small parts this isn't much of an issue.

You don't need any of the sealant chemicals listed, boiling water works fine. You don't need the special dyes listed, clothing dye works fine as long as the part won't be in the sun. You don't need lead for the cathode, aluminum flashing works fine.

In warm weather I use a "double boiler" approach of placing the sulphuric acid bath in a second container of ice water. That keeps the temperature down. This is a very safe process. The acid is diluted to about 1/2 to 1/3 normal strength and the lye solution for pre-etching the parts is very weak. The acid solution can be reused many times and when too contaminated with aluminum you just mix in sodium bicarbonate to neutralize. It is then safe to dump on the ground as it forms aluminum sulphate which is used in fertilizer.

To give you some idea of how weak the acid bath is I test the temperature with my finger and then just rinse it off in the next fresh water bath. It is strong enough to ventilate cotton clothing though so don't wear anything you care about.

05-06-2006, 11:33 AM
Working with the acid and caustic doesn't bother me. We use a similar set of stuff at work every day, except it's a hydrocloric acid to clean steel parts, followed by a caustic rinse to neutralize the acid residue. I also did a fair bit of chemistry in school, and still remember a lot of the basics.

I'm guessing that it's really necessary to use clean acid, 'recycling' likely wouldn't work?

If you want the dye to stand up outdoors, what would you have to do different?


05-06-2006, 02:50 PM
The Yahoo anodizing group has a lot of good information:


I also found this guy's site to be excellent:


I felt the book he sells was well worth it.



05-06-2006, 02:51 PM
You don't want any contaminants in the acid. Even a little iron will cause problems. As for the dye, proper anodizing dyes are colorfast under UV but they cost a lot more than clothing dye.