Metal finishing Q&As since 1989
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Bronze anodizing colour fading
Hello Everyone:
Very informative site!
We are having an issue with a shipment from our anodizer. The alloy was anodized medium bronze, with a hint of pinkish appearance ( twist part in light and it changes shade). As we were installing the parts to our equipment, over a span of 3 weeks, we suddenly noticed that the colour is starting to blotch and fade. Whats being left over, is basically a lighter shade of what is started. We have overhead fluorescent tubes in our assembly department ( could it be the cause?). Anodizer claims to have sealed the parts with a (nitric ?) sealer. He did a quick test, where he immersed the part in hot water. The colour remained the same.
What could be the cause and any suggestions as to what we should ask from the anodizer?
Thanks in advance,
Engineer - Ville St-Laurent, Quebec, Canada
2007
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Most bronze colored anodizing that I have seen is done with a process using ferric ammonium oxalate [FAO]. It's used a lot because the coloring matter is inorganic, hence, lightfast. Perhaps, a dye was used instead, this time?  Dave Wichern Consultant - The Bronx, New York 2007 Questions for your anodizer: (1) nitric? seal or was it nickel acetate which is standard for colored anodic coatings, (2) was organic dye or 2-step process used [organic dyes subject to fading due to light exposure whereas 2-step resists fading], (3) thickness of anodize [amount of color is dependent on depth of penetration whether dyed or 2-step], (4) what is hot water test? only will tell if totally not sealed or very poorly sealed - a better seal integrity test would be ASTM B136. Hope that helps for now.  Milt Stevenson, Jr. Syracuse, New York 2007 |
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