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Aluminum is oxidizing/pitting during the barrel tumbling process

Q. I have recently had a problem with 6061-T6 aluminum pitting when I am tumbling them before taking them to the anodizer. It has happened a few times and the first time I thought it was because I stacked the parts flat after I took them out of the tumbler without drying them good enough. But it just happened to me again and I dried the parts very well and placed them in egg flats with no parts touching each other. This was after a long tumble (20+ hours) but some parts need this long of a tumble to get a uniform finish. Does anyone have any idea if I am doing something wrong or is there a finishing compound I should be putting in with the water to keep this from happening? I am using ceramic media and tap water with some dish soap in a kramer tumbler with a plastic bowl.

Cody Engstrand
hobbyist - El Cajon, California, USA
2007

A. Hopefully you have found your solution by now. Are you certain there is only 1 metal present in the tumbler? If not it is likely a galvanic reaction is taking place during tumbling.

James Endersbee
- Melbourne, Victoria, Australia
January 7, 2008

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