After the 2 hours setup time the flask is placed in a kiln sprue side down for a 6 hours burnout cycle. The initial 2 hours is spent slowly taking it up to 300 degrees F. This dries out the investment and eliminates all water that could turn to steam.

The next step is 1 hour at 700 degrees F. At this temperature most of the wax has melted and run out of the mold leaving a void in the investment where the wax patterns were.

The next 2 hours are spent at 1350 degree F. At this temperature any residual wax is vaporized leaving a clean cavity for the casting.

Finally the temperature is brought down to 1150 degrees F and held there until time for casting. I can start a burnout cycle before going to bed and my programmable kiln has the flask waiting for me at casting temperature the next morning.

Some ppl use a much shorter burn-out cycle successfully. It is a personal thing and I am generally in no hurry. Larger production flasks require longer cycle