Here's a question I was asked recently:
"I'm soldering jump rings on to my fired pmc pendants and I'm having real trouble with the surface of the pmc popping and making bubbles as I'm heating the solder. It was fine when I fired the pmc so I can't understand why it's happening now, any one got any ideas?? It takes so long to make each pendant and they're being ruined at the last stage Thanks!"
Thankfully it's now sorted out and here's the solution for you! :)
The problem turned out to be quenching the fired PMC pieces prior to soldering.
Fired metal clay that has been washed, or wet in any way, can keep humidity for a very long time inside its pores. This is especially true of quenching which seems to force the water into the metal.. If that's the case then the fast heat up with a torch is the problem the moisture is trying to force it's way out.
Try going over your silver clay on it's own and heating it with a more gentle heat to drive out moisture then when soldering try and heat the whole area to even the heat distribution before a final quick focus on the jump ring.
Either that or you'd need to use easy paste solder and be very very quick with a fine flame (so the Metal Clay doesn't get heated)
Hope that helps