As for your previous firescale issues-- usually, a lot of
firescale is actually from too cool a flame, not too hot,
Sorry Noel, I must disagree with you here. Firescale is caused by
the oxidation of the copper in the silver matrix which happens faster
at higher temperatures. If you have adequately fluxed your work you
are actually better off using a cooler flame as it typically will not
have as much free oxygen present in the flame which will then
oxidize or "use up " the flux more rapidly.
You are asking for trouble if your flame is too small (not enough
energy) for the work at hand and this may be the place where this
idea gets started. A properly sized torch flame for each item you
work on is much more critical to getting clean firestain free
soldered work and is second only to proper fluxing in importance to
a successful job. I get absolutely beautiful results with a gas air
torch that is more than 1000F cooler than a similar oxy-fuel torch
flame. A properly mixed propane and air flame burns at 3,622F and an
oxy-propane flame is 5111 F there is no reason for the additional
1489F degrees to melt a solder that is fluid at 1100-1400F (silver
solders). I believe that the vast majority of problems with silver
soldering are from trying to use the Little Torch or its equivalent
on work that is just too large for it and trying to solve the lack
of enough heat energy by using a hotter flame.
If you keep heating and heating over a long time span without
succeeding in really getting the metal hot enough, you exhaust your
flux and get firescale.
You are absolutely right here.
Soldering fast and hot generally causes fewer problems. Provided
you don't actually overheat, of course.
Fast yes but with the appropriate amount of heat energy (Btus) not
temperature. So larger softer cooler flames rather than hot hissing
little flames. Think about all the marvelous work done in years past
(and even today by those trained in its use) with nothing more than
a mouth blow pipe and a fuel gas or liquid fed flame.
Please do not get me wrong I have and use oxy/propane torches and
own a little torch that I am very happy with. The trick is using the
right tool for the right job. I would no more try to do platinum
soldering with my gas air torch than I would solder the spout on a
teapot with my little torch, different jobs different tools.
So in regards to Carol's question I would say a Prestolite or the
Smith equivalent with a full array of tips will be adequate for most
jewelry size jobs. If the money is there than adding a "Y" connector
with shutoff valves to the acetylene regulator and an oxygen tank
with regulator and a Meco Midget or similar torch would allow for
working on anything other than hollowware. Larger work like hollow
ware really requires large flames that are easy to produce with
natural gas - compressed air or propane - compressed air torches but
really not available from other torch configurations. While you can
use large oxy fuel gas torches for this work they are just too hot
and lead to too much firescale and too much risk of melting the
work. The main drawback to compressed air torches is the need for an
air compressor and its attendant noise. But my National 3A-B
compressed air propane torch will produce anything from a monster
flame suitable for hollow ware to a tiny pin point flame for the most
delicate of jewelry jobs. I only use oxy propane for platinum or 950
Palladium soldering or casting.
James Binnion Metal Arts