Ray-Vin Lost Wax Casting Primer
Before you can put the metal into your mold, you must remove the wax. This is a two step process.
First, the mold is heated over water and the rising steam will melt out most of the wax very gently.
This is important since you don't want expanding wax to crack or fracture your investment
and this gets the bulk of the wax out without turning it into nasty fumes!
Secondly, remaining wax residue is burned out at high temperature so there will be no source of gas
when the hot metal goes in. The hot flask will facilitate the molding process.
My rig for steaming is just a tuna can with a couple of rods across the top.
I fill it about half full of water and set the flask on it sprue side down.
This can go into a cold kiln or one that is already at about 300F.
I let it soak in the heat for about an hour.
You can also do this on a hot plate with a pan and a grill. Put the pan on the hot plate and fill it about 3/4 full with water.
Put the grill on the pan and the flasks on the grill with the sprues down. Keep the water at a low boil. Again, one hour should be enough.
After the steam job, the flask can be heated to drive off the remaining moisture and burn out any wax residue.
The book recommends 2 hours at 300F, 2 hours at 700F and 3 hours at 1300F. Then to 900F for one hour and hold it there until you cast.
You can see from these temperatures that you won't be able to do this in the kitchen, in spite of an understanding spouse!