There are several things
There are several things that figure into figuring out the ideal slumping time and temp. Most signficant of these is the unsupported weight of the glass. Large, thick, glass tends to slump faster than thinner, small pieces because there is more unsupported mass on which gravity can pull.
Other things to consider:
– different glass colors melt at slightly different temps
– sharply angled molds take longer because as the glass gets closer to fitting the angles there is less unsupported glass left
– thick glass in a small mold can be tough because there is no place for the glass to “fit” as it melts into the mold
There’s no one right answer for small work. When projects don’t slump as much as I want, I usually will bring my slumping temp up to 1250° F (677°C) and then, if it still doesn’t slump sufficiently, I start adding time. You may have to peek while it is slumping so you know when to end the hold and start the cooling.
Helios Kiln Glass Studio