There are a couple of good articles dealing with casting issues in
the August MJSA Journal magazine.
One of several things that I found interesting was a comment about
burn out cycles and hold times that J. Tyler Teague made about
removing carbon from your flask (carbon residue is the enemy of good
castings). He was saying that the concentration of oxygen goes down
as the temperature in the kiln climbs. That by the time the kiln is
at 1350F the concentration of oxygen in the kiln is at it’s lowest.
He also pointed out that the point were= wax catches fire and creates
carbon dioxide is about 450F. At that temperature the level of
oxygen is much higher than later in the cycle.
He suggests that you soak your flasks at 500F for a an hour or two
because of the flash point of the wax and the increased density of
oxygen (then continue on through the rest of the cycle). This with
give the carbon and oxygen the best shot at meeting up and burning
off the carbon residue.
It’s worth a read,