Oxy-Acetylene torches are lit the same way as oxy-LPG, and yes
oxy-Acetylene is hotter. When lighting the acetylene, a small cloud
of black soot will float through the air until you turn on the
oxygen. A plumber friend of mine prefers oxy-LPG because he does not
want the black soot dirtying his customers houses. A good ventilation
system will solve the soot problem, but in time it will blacken
everything in it's path.
Oxy-LPG will do your melting if you have the correct nozzle. The
most economical solution may be to get a melting nozzle for your
existing little torch set-up. To add acetylene to your system will
require a new gauge or adaptor, a new cylinder, and also a melting
I use a LPG gas-air torch for most jewellery work and a
oxy-acetylene welders torch for melting, fusing, soldering big
silverware items, soldering ring shanks while in the mud bath, and
for making steel tools - forging, welding, hardening and tempering.
Having used a little torch in the past I prefer the two heating
methods described; they are efficient and versatile except for the
soot which ends up everywhere despite the precautions I take.