Anodizing that fades

Letter 16056

Anodizing that fades

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I am a quality control manager working with type II anodizing for the first time. Some of our parts, after being in the field for three months or so, get a lighter color to them going from their original black to a brownish orange color. I believe the problem to be ultra-violet bleaching and I know that it is from a problem in the anodizing process. Is their a cheap and easy to perform test that would readily find the defective anodizing?

Kenneth J. Winward
- Kennewick, WA, U.S.A.

First of two simultaneous responses -- ++

The problem is more likely with the sealing than with the actual anodizing (although it is also possible that a poor quality dye was used, the sealing issue is more likely). ASTM B 136 describes a dye stain test to use to check seal quality on a pass/fail basis. The test requires Nitric Acid (40%) for two minutes and blue dye for 5 minutes, if there is a color change the parts fail (check out the spec for more detailed instructions, make sure to rinse and dry the part in between steps).

Jim Gorsich
Accurate Anodizing Inc.

Compton, CA, USA

Second of two simultaneous responses -- ++

Use the dye stain test on your parts.. its a very easy one. All it takes (in the case of dyed parts) is a 50% (vol) solution of nitric acid. Place a drop on the surface, and allow it to remain there for 2 min. Rinse thoroughly. If a spot remains after rinsing, the part is not sealed adequately, which is what I suspect the problem may be. In the case of clear (natural, for the purists out there) anodizing, one would follow up the nitric acid with a drop of Blue 2LW dye for a period of 5 min, followed by a rinse. If the blue spot remains..then, once again the part has failed. Abrading the spot with Pumice [link is to product info at Amazon] is allowed in both tests. If the spot does not show after a light pumicing, then it has passed.

Marc Green
anodizer - Boise, Idaho

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