A while ago Bob Leatherbarrow gave a presentation to Lunch With A Glass Artist (LWAGA) on slumping schedules. You can follow a recording of the Zoom meeting after joining the Facebook group: Lunch With A Glass Artist – Larry Pile.
The most important point for thinking about the process he brought up is his order of consideration of factors. They are:
- span
- thickness
- viscosity
How big is the unsupported part of the glass. Glass on larger span moulds will begin slumping at lower temperatures.
The thickness has an effect. With the same ramp rate thicker glass will need higher temperature.
The viscosity of the glass also affects the temperature of the slump. Low viscosity glass will slump at lower temperatures than higher ones, e.g., black vs. white.
Then you can begin to think about temperature and time. The objective is to use the lowest temperature to get the slump done in 30 minutes, so there is no marking of the glass touching the mould.
There is a lot more in the presentation to LWAGA. Join the Facebook page by answering two questions to get access.
There is even more information about fusing principles and practices in his book FiringSchedules for Kilnforming, Just Another Day at the Office. This inexpensive eBook is worth much more than the purchase price!
A lot of information is also contained in my e-book Low Temperature Kilnforming, available from Bullseye, Etsy and from Stephen.richard43@gmail.com
