Slumping Temperature and Times

There are two main views on slumping ramp rates and soak times. One advocates relatively quick rates, higher top temperature, and short soaks to avoid excessive marking on the mould side. The other advocates slower ramp rates to a low temperature with a long soak.

I am on the "slow, low, long" side. Bob Leatherbarrow even places the shiny side of the prepared glass down towards the mould, with low temperature and long soaks, checking every 15 minutes on the progress and skipping to the anneal when the slump is complete. This gives two shiny sides.

If a slump can be achieved in 13 minutes, the temperature is higher than necessary. An alternative is to use a lower temperature for 30 minutes or more. Peeking at 15 minute intervals will be necessary to determine when the slump is complete.

The anneal and cool for a tack fused piece should be as for twice the thickest part of the piece at minimum. My experience has shown that annealing a slump for one layer thicker than the calculated thickness produces a piece with less stress than just the simple twice the thickness does.