Clearly there was something in your endcap other than just solder or
silver. There might have been some epoxy, antiquing agent, or human
goo. I would certainly ultrasonic if I could (Can you go to a
friend's and use theirs? Is there a jewelry store whose ultrasonic
you could sweetly ask to soak it in for a while?), but in my
experience when working on "mystery" ethnic jewelry, even the
ultrasonic may not get it perfectly clean, so you may just have to
suck it up, breathe in the nasty fumes and attack it as best you
can. Beware that if you ultrasonic it for an extended period of time,
you'll be repolishing and reantiquing the whole thing. If you
suspect human goo, you could also go the "granny bomb" route and soak
the thing in Drano (lye) for a day. Be wary of stones in the Drano
(diamonds OK), but if you're already torching the piece I suspect
you'll be fine.
Best of luck!
Jalia M. LaNoue Goldsmith Spinelle Fine Jewelers Napa,