Hi Carin -
I can speak to the sterling/18K bimetal that is commercially
available. The gold is five percent of the weight and technically
I use the same torches for this material as I use for regular and
de-ox sterling. If you are joining two pieces, you do need to use
gold solder to avoid a silver solder line. If you don't care about
the line, silver solder works - just use medium or easy.
I pickle the material just as I do sterling, but I protect the gold
when soldering with a traditional gold-working material - boric acid
powder in alcohol. This is a dangerous, highly flammable material
that works perfectly. Just be sure to close the alcohol jar before
you bring the torch anywhere near. I try to always heat the metal
from the sterling side.
In order to preserve the gold material, I always tumble it in a
medium fine abrasive. If you use a regular buff, be very careful -
you remove comparatively much more material with the buff.
The little experience that I have with gold-filled base metal was
unsatisfactory. More practice might generate better results - it
just seemed like the base metal wanted to melt (torch was probably
too hot) and when it did, it burned off the gold. I tried this
material early on in my jewelry career and it might work better now
that I have more experience.