I have various aluminum bits anodized now and then, got one done just last week. I always go with black, but I’ve seen cobalt blue, copper colored, beige, etc. What IS anodizing? How does one change the color of a metal without painting it? I understand doing a chemical patina as in copper…but, this stuff seems a part of the surface of the metals now. Anyone out there with the Straight Dope?
Cartooniverse
If you want to kiss the sky, you’d better learn how to kneel.
Anodizing is the process of running a current through a piece of metal to accrete a thin layer of another metal to its surface through electromagnetic attraction.
He’s the sort to stand on a hilltop in a thunderstorm wearing wet copper armor, shouting ‘All Gods are Bastards!’
Or so I recall. 
The process you describe is electroplating, not the same thing. Anodizing is done with current and an acid bath that forms an aluminum oxide layer on the surface. This is typically only done with aluminum (or aluminium for that matter) because the oxide form is actually harder than the metal itself and fairly corrosion resistant. In pure crystalline form aluminum oxide, also known as sapphire, is second in hardness only to diamond. colors are done with dyes that stick to the porous oxide layer.
I stand corrected
Sure, I’m all for moderation – as long as it’s not excessive.
Padeye has it pretty much nailed, but if you want more info and the gritty technical poop, click this link for the high points of MIL-A-8625F.
That sounds painful but I think a little extra fiber in your diet might take care of it. 
Terrific link UncB. It’s one of the most informative I’ve seen on the topic.
The scary thing is, I was able to pull the MIL-SPEC number from memory, even though I haven’t specified anodizing for several years. Anybody up for chromate conversion MIL-C-5541, or perhaps a nice black oxide coating, MIL-C-13924? How about some electroless nickel, MIL-C-26074?
What is the difference between alodine and alodide maybe its anodide Can’t remember but we used two aluminum coatings.
Alodine is a trademarked name for thc chromate conversion mentioned above. I haven’t heard of your other two terms or been able to turn up anything with a web search. Neither, are they in my materials handbook.
Thank god I didn’t ask about the difference between Powder Coated Anodizing and Hard Anodizing, huh? Thanks all ! And for what it’s worth? I never noticed that the cobalt blue anodized bits I have, and use, wear down any faster or slower than the black anodized bits. They are very durable. Yes, the black coating IS harder than the metals underneath.
Thank you for the Straight Dope…god bless you one and all.
Cartooniverse
If you want to kiss the sky, you’d better learn how to kneel.
Not sure of the name any more. We used two different coatings in Navy S&R work. circa 1970 There would have been a mil spec on it .Don’t make any difference now. They probably have a powder coating for it now.
Just reminiscing.Thanks