dabac

Hi all,

I came across this seat post with a partial bronzed sheen to it.
Question is, has it faded from the original black anodizing, or has it been painted?
Neven seen black anodizing turn bronze before.
OTOH, if it'd been painted after purchase, I'd expect that the paint would have gone over the warning sticker as well.
I can't imagine anyone removing a sticker - carefully - prior to painting and then putting it back on.
Particularly not the same guy who left the reflector clamp in place while applying the paint.
Also, the clamp didn't have a speck of paint on it.


Any suggestions?

alcjphil

Maybe the other way around, bronze anodizing turning black, or maybe black paint over bronze anodizing.

Andrew R Stewart 

The OEM coating was most likely black anodizing. Sun light will fade some anodizing. The bronze matches what a few of my parts have become after outside storage for long periods. This is of no worry but cosmetic. Andy.

dabac

But why would it turn black under the band and in the seat tube and not on the exposed parts?
And how come the black saddle clamp has such a razor-sharp edge from the black to the bronzed?

Booger1

When you anodize with Koolaid.......it turns colors in the sun....

I've had the same happen on some stuff,black to bronze looking.Cheap sun faded anodizing.

fietsbob

you have it backwards ,,what was clamped on remained black, while the rest of it likely bleached in the sun to bronze color
the head** was painted and bonded into the tube shaft,. or perhaps just in the shade under the saddle?

You Can always buy a brand new seat post, of the same shaft diameter..

**Cast "Laprade/ Kalloy" ( low budget ), Shaft, a tube of different Alloy

dabac

Bronze-to-black was Alcjphil's suggestion, not mine.
And yeah, I realize replacement is an option.
But while I've seen black anodized parts turn grayish before, turning bronze was a new one to me.
And if it was the shade from the saddle keeping the clamp black I'd expect more of a gradual transition. Either clamp and post were anodized separately, or they are different alloys that take color differently well.

dabac

Koolaid anodizing, intriguing.
Don't think that is quite the case here though, as the sticker is still in place.
But cheap, yeah, that's certainly a possibility.

ctpres

My aero bars started out black when new last summer. Bike only outside or uncovered when riding and now I have one bronze or almost gold looking bar and one black bar. So I would say it is mfg. defect in the finish.

Booger1

Just joking about the Koolaid but you CAN anodize at home with Ritz dye and a battery charger!

FBinNY 

Black anodizing is very UV stable (done right), which is why it's suitable for all sorts of outdoor applications. But is is vulnerable to various forms of chemical and mechanical attack (abrasion). Looking at the pattern, I wonder if maybe you had a seat bag strapped there, which trapped chemically laden road water against the post. The water will dry, but the chemicals are left there and can discolor or remove the anodizing over time.

dabac

IAFAIK, no saddle bag. The black band is from a reflector clamp. Poor quality seems like the most probable cause. Strangely enough, the stem has taken on a similar hue. Kinda improbable that two different parts on the same bike would have the same manufacturing flaw.

Kopsis

It's just cheap anodizing. Here in Florida, it's extremely common for black anodized parts to turn bronze. There are anodizing solutions that have good UV resistance, but their use on commodity parts sourced from China seems to be the exception.

rico_mack

What Kopaia said, although I'm not sure I would say it was "cheap" anodizing. I had a Control Tech quality seat post do the same, i.e. turn from black anodizing to a bronze color, after being in the blistering southern AZ sun.

cyccommute 

Some black anodizing is UV stable but others are not. It depends on the dye used in the anodizing process. Some of the older dyes (mid 90s) were very unstable. I've seen old parts are my local co-op that are completely silver except where they had a clamp of some sort on them. They have changed the dyes used and gone to a different coating method since the mid 90s that are more UV stable.

The decay of the color isn't related to water either. Water containing salts...the only "chemical" used on the road that might damage the anodizing...would result in pitting of the seatpost not simple removal of the dye. The post would look a whole lot worse if it were damaged by salt. This is all photochemical.

cyccommute 

Probably not. I've seen this kind of fading on some very expensive parts. Most bikes with really high end parts don't spend much time in direct sunlight other than when being ridden...most people aren't likely to leave a $2000 bike outside for much longer than a ride.

Wilfred Laurier

The stem on my wife's mtb is similar to that bronze colour. It was black sometime in the past.