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I have recently had 4 screen melts crack. Two had one clean crack and the other two completely shattered. I am trying to make a 12 inch round, 3/4 inch thick, using spectrum. I am melting into a stainless steel ring lined with fiber paper. My schedule is:
800 to 1600 hold 90min
9999 to 1475 hold 30 min
9999 to 960 hold 60 min
200 to 750 hold 0
50 to 300 hold 0
Please any suggestions before I was anymore time and money.
Thanks in advance
Brandi

Anneal for a MINIMUM of one hour per 1/4" of thickness.
Look up Clearwater Glass and compare his schedule.

Mr Immerman is so generous to post these to help people: http://www.clearwaterglass.com/Tutorials/MeshMelt.html

Hi Brandi,

You might want to check out S96 firing schedule for thick projects: http://www.system96.com/Pages/ThickFiringGuideF.html
I think you need to do some work on the annealing and cooling portions of your schedule. 3/4" is a pretty thick slab and you'll need to slow your schedule down quite a bit.

Best of luck with this!

Sharol

Why are you using 960F to anneal??? it has been listed at 950F (according to "96" documents for several years)

yours ours
9999 to 960 hold 60 min 9999 to 950 hold 3 hours
200 to 750 hold 0 100 to 850 hold 1 hour
50 to 300 hold 0 100 to 750 hold 1 hour
100 to 600 no hold and off - let cool totally to room temp before opening


This is works for us.

sorry that came in so hard to read - this is better
9999 to 950 hold 3 hours
100 to 850 hold 1 hour
100 to 750 hold 1 hour
100 to 600 no hold and off - let cool totally to room temp before opening

Don't hesitate to re-use your shattered pieces in new melts/pieces. That's part of the joy of fusing!

I agree with Laurie on the three hour soak at 950F.
However I disagree on the soaks during the annealing cool. The principle is to reduce the temperature gradually enough that the whole of the glass is within a few (+/- 5 deg) throughout. This in my view is better achieved by a slow consistent cooling rather than a cool followed by a soak. I am not sure that what will happen on a quicker cool will be cured by a soak.
So from 950F I suggest a rate of 45F/hr to 850F, on soak; then 80F/hr to 650F, no soak; followed by 270F/hr to room temp[you have no idea how hard it was to put this into F rather than C].

I am also wary of using the old melt pieces, especially if they are hot colours, as they tend to change characteristics after high temperature firings. But only testing will prove.

Maybe the reason that this schedule works for us is that my kiln cools very slowly. For instance last night i had a look and it was 800 at 11 pm and this morning at 8 am it is 450. In a fast cooling kiln i would agree with your caution.
I should have added the footnote that every kiln fires differently so you have to get to know your own kiln. I have 6 and they all fire quite differently! Thanks Stephen for reminding me........ maybe that should be part of a signature line?