You never need holes in a
You never need holes in a draping mold. You often, but not always, need holes in slumping molds.
Holes allow air, that would otherwise be trapped, to escape from between the glass and the mold. That air expands during the firing and makes it more difficult for the glass to drop.
Very shallow molds usually do not require holes.
If you have a choice, take the holes. They won’t hurt anything even if they end up being unnecessary.
Helios Kiln Glass Studio