Metal Clay Jewel-ers tumble their jewelry all the time. It does work
harden the fine silver a bit and polishes it up very nicely if
that’s what they’re after. It doesn’t seem to me that you have much
experience with metal clay Steve. It’s a much hardier material than
you seem to think.
Sterling silver posts can easily be soldered directly to the metal
clay. The fired item just needs to be burnished first so that it
doesn’t soak up too much of the solder. I’ve been doing it for years
with no failed joins yet.
If you really don’t want to learn to solder you can buy the posts
that have a 1mm pad and embed them in PMC3 and fire no higher than
1250 for 45 minutes. Any higher than that and the sterling will
become brittle. Yes, the 45 minutes is a bit of overkill, but metal
clay when fired at low temperatures does better if left to soak for a
longer period of time.
There’s a soldering for metal clay video on the new Ganoksin
BenchTube site, another at PMCGuild.com and one on You Tube.
It’s not as intimidating as some new jewelry makers might think.