SLUMP with BULLSEYE (6mm)
1. Initial Heat (Process Soak) 155/hr to 704C 0.20
2. Rapid Cool AFAP or 9999C/hr to 516C 1.30
3. Anneal Cool 26C/hr to 371C 0.00
5. Cool to room temp. AFAP or 9999C/hr to 25C 0.00
Afraid I have to disagree with this schedule for a simple slump. Bullseye reccomend 638 for 10 minutes for a slump. I have found that 630 is quite adequate to slump 6mm over a plate mould. Going as high as 700 will cause the glass to become liquid enough to start flowing over the mould. For something like a plate this may cause the edges to bow in or the centre to be pushed up.
Every mould is different and will need different temperature and soak.
Having just tried this, I'd say that schedule was spot on! I started with a more conservative top temperature (660C - it didn't budge at all at that temp), but needed to go to 730 for the thing to slump. Even then, it needed the 20 mins. This probably does depend on mould and other factors, so starting with the more conservative temperature but being aware that you may need to increase it if it isn't enough might be the best thing.
For what is worth, for a plate or shallow bowl I go to 650C and hold for ten minutes - but it will also vary from kiln to kiln as well as from mold to mold. I don't cool afap after annealing, I come down at 100degrees/hr to 100C. I found that bullseye tech notes were very helpful as they give the temperature ranges for when you can expect slumping, fusing, etc to happen. They can be found here: http://www.bullseyeglass.com/images/stories/bullseye/PDF/TechNotes/technotes_04.pdf
That's a really good link, explains a lot - thank you :)
That is a fab link, i feel like i just learnt a whole heap (and i don't fuse...yet!) ;) ;D
Great posts. Bullseye tech notes are really useful.