I have used the propane and flowerpot many times....though I prefer
an open coil electric hot plate. Be sure the porpane tank is full
and, at full on, it should run for about 2.5 hours. Make sure the
flower pot is covered by at least two layers of heavy aluminum foil.
Re the sprue....8 gauge is much too large and remember, you can only
do one flask at a time and it cannot be too large. I usually use old
tomato paste cans as a flask. If the sprue is too large, the metal
will sagg down into the sprue and go into a semi-hardened state,
blocking the remaining metal from entering. I normally use two or
three (sometimes even 4) narrow strips of 20 ga wax sheet placed
closely together (about 1/2 mm between them). That way, the metal
will not loose its surface tention and sagg.
An alternative way to heat the flask is to use a charcol 'starter'.
This is a stainless device obtainable at most 'outdoor' shops. It is
thin metal, about 4-5' around with a piece of screen inside about 1/4
up from the bottom and a wood handle on the outside. Place about a
dozen briquettes into the device then the flask, then fill it the
rest of the way wit briquettes. Light this off and wait about 2 to
2.5 hours. Does a great job.
Cheers from Don at the Charles Belle Studio where simple elegance IS