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Black anodize gets white stains only on large sheets

none is made possible by ...
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Q. I have been working in an anodizing shop in Texas for 5 years. We have a great finish except when I have to black anodize big panels (40 in x 40 in) there are some white stains.


I mostly have small pieces and all of them looks great ... but with big panels I always have troubles.

I checked the anodize and the aluminum concentration was good, the sulfuric concentration was good, also the temperature and the voltage.

I just changed my desmut and ETCH and added black dye to the tank but this keeps happening.

Do you know why this happens?

G Cazares
- Garland Texas
October 11, 2023

A. C Cazares,
It looks very much like a rinsing issue. The center area of flat panels is always the last to rinse free of chemistries. Add or increase the amount of agitation in the rinse along with extending rinse duration. Repeated in/out up/down cycles of the rinse will help on larger panels such as the one shown. Spray rinsing may help but it would need to be more than just a few passes with a hose.

Willie Alexander
- Green Mountain Falls, Colorado
October 23, 2023

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