Flattening before Slumping works Best

[Red_Jello]

I agree with Terri in that you may acheve a better result if you “flatten” the bottle with heat before a slump firing.  The temperature you listed in your firing schedule is sufficient to flatten it, but lengthen the time of the hold (by 5-10 mins depending on your kiln). Each kiln is different, so test fire & take notes.  Use the schedule that produces the best results for your aesthetic.

Your slumping temp doesn’t nearly have to be that high.  Depending on your glass properties & size, your slumping temperature should be  around 1200-1300 degrees and held for about 20 mins.  Don’t foget to kiln wash your molds.