You want a little moisture. I always let mine sit overnight before I
load them. If they’re going to sit much longer than that, I put them
in a plastic bag with a wet paper towel. Never had a problem in 12
years of doing it that way. Usually let the student flasks sit for a
week between investing and burnout. (in a bag, with wet towel.)
If you’re going straight for burnout, the last time I read the
directions, they said to let them sit for 2 hours after gloss off
before you move them.
I have had issues with flashing once or twice when I was forced to
move them early. Patience is a virtue when it comes to casting.
Meanwhile, why are you worried about steam hurting your kiln? If
it’s gas fired, it’s an overgrown BBQ grill. It’s basically a brick
box, with a torch under it. What’s it going to do?
If it’s electric, it’s a brick box with coils of hot wire. Water is
going to flash to steam and get out of there fast. The real killer
for electric kilns is the carbon soot from the wax. Turns out carbon
soot is conductive. Stuff enough flasks in there that the soot gets
dense enough, and you can cause arcing between the coil loops of
your elements, and burn them out. (Ask me how I know this…)(Hint:
it has something to do with why I know how to re-wind kiln
elements…) This is one reason I really like the old Neycraft
fiber furnaces: the elements are buried in the walls, and shielded
from the burnout. MUCH tougher design than the open coil kilns, if
more expensive. If you’ve got one of those, you’re bulletproof.
Steam isn’t much of a risk. It’s looking for a way out pretty
aggressively. The water comes out of the flasks slowly enough that
the density never gets high enough to do much.