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Early 80's Alloy Bicycle Parts Anodizing

Greetings:I am a collector of late seventies and early eighties BMX bicycles. The attraction and much success of the bicycles was based on the introduction of alloy parts to the consumer markets in the late 70's. Almost all of the then parts mfg's are long gone. However, the parts are still in really high demand even in used condition as they can be restored. The parts command very high dollars sometimes as well.I am currently restoring some stems that are made from 2024 aluminum. I went to my regular anodizer and they usually can do a really nice deep red. This last round however, the parts are coming out somewhat pinkish in color.My parts are polished prior to the anodizing process. Why is it shops are so quick to complain about the material all the time? Can 2024 be processed to look similar to 6061? I live in Southern California. Are there restrictions that make the shops use the same dyes?It seems like depending on the weather (pun intended) the shops may or may not do a good job. Is the quality of labor a factor in my area?Last question, can I perform anodizing on small parts in my garage?Thank you very much for reading this. I am out hundreds of dollars in "min" charges per color along with some rare parts being damaged. I cannot afford to go any further with these shops.Thank you for reading this.

Mike N [last name deleted for privacy by Editor]
bmx stuff - California
2005

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Hi, Mike. That's a long multi-faceted question, so the answer will be long as well :-)When parts come out pale or pastel rather than vivid, although the problem could be a weak, off-color, or exhausted dye, it's probably more likely that the anodizing isn't thick enough to get a vivid color. An anodized finish is like a honeycomb at a much smaller scale. The dye is absorbed into the pores in the hexagonal structure and then the pores are sealed so the dye stays in and dirt won't go in. If the anodizing is thin, the amount of dye absorbed is small and the color isn't saturated.But why is the anodizing thin? Probably because of the specific alloy. While 6061 is a good anodizing alloy, 2024 is a very copper-rich alloy. Only aluminum can be anodized into translucent aluminum oxide, the copper will just turn gray or black. Although you can "desmut" before anodizing to remove the copper, this is only a surface effect, so getting a thick dyeable (transparent) layer of anodizing is very problematic with 2024, perhaps impossible. If you've tried several shops, it's not the dye or regulations on the dye, it's the alloy.The quality of labor is a problem in every industry and everywhere in the country, Mike :-)There are many people who do hobby anodizing. There are safety and environmental issues involved, but if you are not selling parts or selling the anodizing service, you are not a business so at least you are not a federally regulated metal finishing business. Although that doesn't mean there are no enironmental requirements, it does lessen them and mean you won't be harassed to madness like anodizing businesses are, and it means you probably won't be inspected. There are local and sewer authority regulations, of course.I am not an apologist for shops who may have done poor work, but I suspect the problem is the alloy, not their dyes or workmanship.Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 31, 2008