I have a copyright 1975 copy of "The Oxy-Acetylene Handbook"
published by Linde, a division of Union Carbide that used to be the
big name in Acetylene. It uses the old term “blowpipe.” This book
gives the following instructions:
In general, the procedure following in lighting a blowpipe is
first to open the blowpipe oxygen valve a small amount and the
blowpipe acetylene valve either fully or somewhat more than the
oxygen valve, depending on the type of blowpipe. The mixture of
oxygen issuing from the blowpipe tip or nozzle is then lighted
by means of a friction lighter, or stationary pilot flame.
"After checking the acetylene pressure adjustment, the
oxy-acetylene flame can be adjusted so as to have the desired
characteristics for the work at hand by further manipulating
the oxygen and acetylene values, according to the
manufacturer's directions for the particular type of
blowpipe." Further on: "When welding or cutting is to be
stopped close the blowpipe acetylene valve, then the blowpipe
The illustrations accompanying the above statements show typical
oxy-acetylene welding torch handles such as those sold by Smith.
Smith torches sold for jewelry work look very similar to welding
torch handles except that they are slightly smaller in size. They
function the same way, however.
I have quoted the above in detail because most silversmithing
instructors say to turn the acetylene on first and off last. I have
never heard these instructions as it always produces the clouds of
soot that you mention.
I would be interested whether anyone on this list has some
"authoritative" reason for reversing the procedure or are these
simply “old wives tales” with no basis in logic.
I generally use air-gas torches for silversmithing and reserve my
oxygen-acetylene for gold work. I think air-gas torches are more
forgiving and easier to control, particularly on silver where you
generally need to heat up the entire object rather than just the
joint being soldered. I realize that some experienced gold and silver
smiths use oxy-acetylene for all their work but a beginner my find
the air-gas torches easier to use on silver.
Hope this helps:
Fred R. Sias
Woodsmere Press, LLC