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Different types of gas

Can someone explain what the different types of gas there are
available, and what are the advantages/disadvantages of each one.
What does the oxygen do? I work in base metals using butane gas but
I presume for gold/silver /platinum I would need something else.

Oxygen is added to fuel gas to make the flame hotter, cleaner, and
forces the fuel gas into a cone. Depending on whether you are
forcing the oxygen- with a cylinder of it’s own, or drawing air from
the atmosphere, is how you get your various flame intensities. It’s
all about ratio. So many parts of oxygen and fuel create different
types of flames… more oxygen makes an oxidizing flame- very hot,
loud and I’m sure there is a reason for it to be used, but I’ve
never had one. Fuel flame is enough oxygen to clean up the fuel,
but the cone is long and quiet. This is a good flame for casting as
it doesn’t overheat the metal and cause oxygen to incorporate into
the melt. This can cause porosity. he neutral flame is the one I
use the most. Just enough oxygen to draw the flame- into a nice
tight cone, but not hissing, and not too long. This flame works for
casting and soldering. When I was first learning to solder I learned
with a “Smith” air/ acetylene torch. The torch draws atmospheric
air to balance the fuel flame. It only creates a neutral flame.
This is plenty hot for casting and fabricating in silver gold and
brass, not platinum- you don’t want a “dirty” gas like acetylene
around platinum. When you add oxygen to acetylene, it devours the
carbon- but it still is not the cleanest gas, but it’s very
predictable. I just added a propane and oxygen setup to my
workshop- the advantages are… when using the forced oxygen and
propane, just as hot as air/ acetylene- it is cleaner, and a touch
more versatile as it is clean enough for platinum, and the propane
is cheaper and more readily available. Acetylene is a more unstable
fuel as well. You can’t get as precise a flame as with acetylene
though, so I still use my air/ acetylene torch quite often.

What tip were you using to cast with this torch? I just bought a
Smith torch that was included in a regular package, but all the tips
are for acetylene.

I don’t know which Smith torch you are using, but I use a Smith
"Little Torch" and use the same tips for both propane and acetyline.
Works fine.

Jerry in Kodiak