Classic & Vintage - Really strange anodizing aging and/or reaction to something.

Bars and stem are from 80s mtbs, Specialized stem and straight bar from one bike, riser bar(unmarked) from another. Where the grips and levers were, brake and thumb, the ano is now black in the exact same areas covered. Furthermore, the Specialized stem(black where inserted) and bar exhibit a fade pattern, from the original ano to a bronze color, on their underside(protected from the sun). Weird! I'm looking forward to enlightenment.

thanks,

Brian

What do you clean it with?

I was about to say the same thing. Some cleaners, drilling/tapping lubricants will turn aluminum black very quickly.

You have it backwards, the items are now NOT black where the sun hit them, and stayed black where they were covered.

Yep, I remember seeing faded anodized parts on bikes back in the 70's and 80's. Even new bikes the hubs will turn rootbeer colored if left in the sun too long. That's one reason I bet original anodized BMX parts bring such a pretty penny now if they're in good condition. Even stored by a window inside a garage for 20+ years, it will fade.,,,,BD

this is pretty common, especially with black anodized aluminum...why?
Because ALL the colors are achieved by adding dye to the chemical bath during anodizing. Black is a particularly hard color to get in a pigment: it's usually very, very dark brown, purple, or blue...so dark it looks black, until... the sunlight fades it, as it will to any dye.
Since you're in SB, and we assume the bike parts in question have been, too, it could be a combo of both sunlight (direct or reflected, most dyes aren't very light-safe) as well as salt air (which might have opened up the surface of the anodizing and accelerated the fading). In any case, it's a pretty extreme example of fade, but not so rare in SoCal.

Yup. What he said.

Just wondering if the paint on the bike faded also...

Could this also happen with black chrome?

The sun will do that. I have many examples of this in the garage.

I seem to remember reading (BikePro catalog?) that anodized parts are dyed AFTER anodizing.

Anyway, it's like unworthy1 said, the sunlight fades black to a lighter shade of a different color, perhaps because certain color elements of the black dye are more succeptible to sunlight fading than others.

I've seen a lot of different fading effects, but the lighter brown is common. Some alkaline cleaners will also attack dies or the annodization itself.
Some color-anno parts bleach out in a relatively short time, like a year or two.

Could this also happen with black chrome?

It may depend upon the quality of the chrome, but in my (admittedly limited and strictly anecdotal) experience with the black-chromed rear triangles of '86 Schwinn Pelotons, no it will not. I've even had one frame that had some yellowing of the white painted main tubes, but the black chrome remained impeccable.
Curious to hear some other anecdotal experiences on this...

Thanks to all for the responses. I just started buying a few 80s mtbs as donors for city/commuter bikes for friends, first time I've come across this.

Brian

I'm not sure I agree that sunlight is the cause, but I do think it's some kind of reaction the environment where the bike was kept (maybe ambient light + oxygen?) I've got a stem from a High Sierra with the same fading (and it's still black where the stem was inserted in the fork.) The fading is so even that I don't think it was faded by the sun unless someone has been turning it upside down regularly.

@zandoval - I agree with calamarichris on the black chrome, my High Sierra still looks good and doesn't look any darker underneath the clamped-on front derailleur. Oddly though, the fork is noticibly lighter in color than the frame. I bought it used, so I'm not sure if it came that way from the dealer.

UV.

I used to do anno for work.


I'm not sure I agree that sunlight is the cause, but I do think it's some kind of reaction the environment where the bike was kept (maybe ambient light + oxygen?) I've got a stem from a High Sierra with the same fading (and it's still black where the stem was inserted in the fork.) The fading is so even that I don't think it was faded by the sun unless someone has been turning it upside down regularly.

@zandoval - I agree with calamarichris on the black chrome, my High Sierra still looks good and doesn't look any darker underneath the clamped-on front derailleur. Oddly though, the fork is noticibly lighter in color than the frame. I bought it used, so I'm not sure if it came that way from the dealer.