A request for suggestions on how to slump found glass that had been shaped by some method was received. The request included a schedule for flattening - open side down – in a mould.
I would not attempt to do both the actions in one step. Flatten first, slump second.
Before you start the flattening, clean it well, as any dirt trapped will be permanently imbedded.
During the slumping onto a flat surface, watch to see when it slumps during the flattening. When the form definitely begins deforming, note that temperature. The rate of advance should be moderate – no more than 150C per hour.
Observe the progress of the slumping. When it begins to deform and change shape this will give you the slumping temperature. Record this temperature as this will be the temperature at which to conduct the slumping of the flattened form.
The temperature at which the deformation begins, minus 40C, can be taken as the middle of the annealing range. This will give you an idea of the annealing temperature as this method is not exact, but good enough to get an adequate anneal. You can begin your annealing at this temperature without worry of it being too high.