Metal finishing Q&As since 1989

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Complete loss of coloring on anodized(?) aluminum hinge

 

We purchase an aluminum butt hinge for one of our windows that we believe to be anodized (dark bronze color). In the Phoenix area, we have encountered some hinges in the field where one side of the hinge completely lost its coloring, but the mating part was unaffected. The hinges are exposed to the exterior of the house and most probably were in direct UV exposure. Is this possible on an anodized aluminum part? What could be the cause for this? We examined the part and it is most probably not a painted extrusion (we did a scratch test). There is no flaking of finish anywhere on the part. The back (unexposed) side of the hinge looked as if the color was beginning to fade. The windows themselves are anodized aluminum (6063 alloy) and we have never experienced this color loss with the window extrusions.

Tony Kubik
- Tacoma, Washington

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Some dyes are organic and not particularly resistant to fading in sunlight, whereas others are inorganic. But if a dye is not properly sealed it won't last long, and that's what it sounds like.

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

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Assuming the parts were, indeed, anodized.. its a pretty easy one to answer..they weren't sealed properly. One other possibility is that the dye the coater was using had a very poor light-fastness rating.

Marc Green
anodizer - Boise, Idaho