Patches of unfired clay on surface

Hi,

I'm new here. I have been working with Metal Clay for a couple of years on and off.

I just torch fired my first two pieces of Art Clay Silver Slow Dry. I've torch fired PMC3 before with success, but I had a problem with this firing.

After firing I had a patch of unfired clay on the surface of each piece. The pieces are solid pendants about an inch in diameter and the patches were round areas about 1/4 inch in diameter. I've never seen this before!

At closer inspection, and after a little scraping I found that on one of them the unfired clay went deeper than the surface so now I have a gouged out area.

I am refiring them in a kiln now, but does anyone know the cause of this?

After refiring in the kiln, can I refire again using oil paste to fill in the low areas?

Thanks,

Virginia