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topic 9802

Film Formation on Black Anodize


My shop is having a problem with a whitish film formation on our black anodized parts. If the parts are reworked, the film does not appear. The film forms every time with the first generation work and changing/varying the etch, bright dip, desmut etc. has very little effect. Any ideas?

Victor Waldman
- Naugatuck, Connecticut


Are you stripping with chromic-phosphoric and running a chrome-free desmut? There are some stains and problems that only seem amenable to removal in chromic acid.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


We are a chrome-free shop so we don't even have the option of trying your suggestion. {:(] The film formation is less if we run the parts with NO pre-treatment, though not as film-free as the reworked parts.

Thanks for any feedback.

Victor Waldman
- Naugatuck, Connecticut


Have these parts been finished in a vibratory system? The ceramic stones create a powder that, if not rinsed off completely when wet, will stick to the surface. This dust is hard to see on bare aluminum and very difficult to remove. The anodic coating will form under this powder, leaving a white residue on the finished part. Stripping seems to remove it. Ultra sonic cleaning is fairly effective in rewetting and removing the dust before anodizing. The best solution is to completely rinse the parts after vibratory finishing.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.
supporting advertiser
Wadsworth, Ohio

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Do you find this situation after the dying or after the seal? We have found if our seal dies prematurely, a white film will form.

Bill Smith
anodizing shop - Trinity, North Carolina

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