What precisely is the problem with a gas bottle? There has been a lot
of discussion about the safety of gas and I would argue a fair bit of
irrational fear as well. With a modicum of knowledge and the use of
fairly standard safety procedures in setting up and running a gas
torch it is a safe tool. Casting, etching, plating, polishing or even
using a flex shaft all have their risks and require skill and
respect. You could consider using a laser or arc welder but these
are extremely expensive and apparently don’t always work well with
silver though they do work well on gold and platinum. I suppose you
could also consider using a water torch that generates it hydrogen
and oxygen on demand but these are also rather expensive though
within limits apparently work well.
Alternatively continue with propane and do so safely with good
equipment properly set up.
All the best