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Green "stain" on Black Aluminum

February 23, 2009

Greetings once again, and thanks for all of your help in the past. This time I've stumbled across a problem with our anodizing line. We are seeing green stains on our black aluminum parts (6061). The stains look like something that has dried onto the surface of the parts, and, with a little bit of effort, the stains will rub off. We're using Sanodal Deep Black HBL Dye from Clariant.

We do not see any evidence of oil in our dye or rinse tanks, and we do not see as much of the staining on cast aluminum. Has anyone run across something like this before? What is it? How can we get rid of it?

Thanks again for your help.

Michael Costello
Plating Engineer - Grand Junction, CO, USA

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First of two simultaneous responses --

My guess is that you are not getting a perfectly clean part in the prep line. Oil in any tank prior to the dye tank can cause grief. The deox/desmut tanks caused the most problems in anodizing that I was around.
Your dye is as good as there is if you maintain the quality checks on the tank and the dyestuff.

James Watts
- Navarre, Florida
February 25, 2009

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Second of two simultaneous responses --

If the nickel acetate seal pH is above 6.0, the nickel falls out, then when the water evaporates a loose light green nickel haze is visible on the surface. So re-standardize the pH meter and lower the seal pH.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

February 26, 2009