From a previous post:
Selecting the proper fuel to cast platinum is of utmost importance.
Do not use acetylene, since it has a very high carbon content and
expels carbon in the flame. The platinum will absorb the carbon,
leading to contamination and brittle castings.
Although propane, or LPG, is also a carbon-based fuel, it does not
have the high carbon content that acetylene does, and therefore can
be used for platinum casting. Be aware, though, that even when mixed
with oxygen, propane does not burn as hot as hydrogen and thus
requires more time to melt the platinum. This longer melting time can
lead to porosity caused by gas absorption or debris - a direct result
of keeping the metal in the melting crucible too long. If you do use
propane, pay particular attention to the flame: It should be no
larger than 6 inches with a high oxygen setting. A sample regulator
setting would be 5 lbs. of propane with 40 lbs. of oxygen.
The most efficient way to melt platinum is with hydrogen combined
with oxygen. This fuel is carbon-free, and the high heat created by a
proper hydrogen/oxygen mix melts platinum in seconds. But even with
hydrogen, a proper flame is crucial: If it’s too big, the flame will
heat the surrounding crucible, adding to the melt time-and creating
the same problems as those with propane. Use as much oxygen as
necessary to make a relatively small but oxidizing flame. A sample
regulator setting here would be 50 lbs. of hydrogen and 50 lbs. of
All fuel gases are dangerous, and you should have a professional
install your torch systems and fuel tanks. In addition, the regulator
on the fuel tank should have a directional flow restrictor, which
allows gases to leave the tank but not re-enter. For safety, use only
regulators designed for the fuel you’re using.
It’s good practice to install hard pipes near the casting machine,
so you don’t have gas tanks close to the heat of the flame. You can
then attach rubber gas hoses from the hard pipe to the torch. These
hoses should be inspected regularly for leaks and wear. Also, always
turn off your regulator and bleed your hoses after use.
This is especially true if you’re using hydrogen; the molecules are
small enough to seep through even a new hose, causing a fire hazard.
Also, when using propane, remember that it weighs more than air and
can accumulate on the ground if it leaks.