What is the Reaction of Metal Clay with Aluminum?

Over the years I’ve been told not to place my moist metal clay on aluminum or there would be a reaction, so I never have. With that being said, I don’t know what the reaction is! Inquiring minds want to know now! I tested PMC3 and the new Sterling Silver metal clay to find out. 

I placed a sample of each clay on aluminum foil and also samples on an aluminum pan. I cut out a total of four oval discs labeling the discs that are laid on top of foil with an F and those laid on top of the pan with a P. I allowed them to sit there for an hour, until they were fairly dry. 

PMC3 & PMC Sterling on pan

PMC3 & PMC Sterling on foil

The two samples on the foil had a huge reaction as did the foil. 

Reaction to foil

Foil's reaction

The two samples on the pan had less reaction. 

Reaction on pan

Fired and polished sterling silver

It looks like the combination of moisture, clay, and aluminum causes the reaction. The PMC3 clay on the pan had less moisture and so had little to no reaction whereas, the foil seemed to trap the moisture between the clay and foil. I fired each sample per the manufacturer’s directions on the corresponding packages to see if the reaction area would burn clean. It did not. 

Fired and polished PMC3

After polishing each sample, the reaction areas are raised and extend past the surface of the clay. It gives the clay a look of reticulated metal. So, if you want a cool looking texture, now you know how to get it. Otherwise, keep the clay away from aluminum.