I make a very thick piece (8 X 10 in.) using Spectrum. It grew to about 1/2 thick because I needed to make sure that some mica inclusions were completely covered. It fused nicely. I trimmed it a bit and fire polished it. So far so good. A few months later I got around to slumping it in a simple square slumper. I followed the firing schedule for 1/2 inch glass I got from the Spectrum website but ramp up #3 was not specified. I tried to figure out an appropriate ramp and target temperature. Needless to say, I chose WRONG.
Firing Schedule:
100 300 15
250 1050 10
150 1245 I checked at 10 minutes and the piece was already cracked and slumped. I annealed anyway.
9999 950 90
100 800 10
300 100 0
Brad's book said to go slower if a piece had been previously fused and if it is thick, but I'm not sure how much slower I should have gone. Perhaps I should have slumped at a lower temperature, but I'm not sure how much lower I should have gone. Any advice would be appreciated.
I'd like to salvage the glass. The bottom layer is blue aventurine. The next layer consists of pieces of lavendar opal and pieces of clear smeared with mica mixed with glass tac. One top is the equivalent to two layers of clear. I thought I would dam the two piece on two side to try to keep the two pieces close to each other and then bring it up to full fuse temperature and just let the whole thing seek a 1/4 inch depth. Will the mica make a mess on my shelf? Should I do this directly on the shelf or should I use Thin Fire? Should I not even attempt this?? Any other suggestions??? Thank you in advance for your input.
I would have fired this 100 degrees an hour up to at least 800. At that point I do not worry a thick piece cracking. I think the increase was just too fast.
What I would do.......others will have other opinions of course.
I would clean it well and then put it in a 8 x 10" stainless steel ring with 1/8" fiber paper lining it on a kiln washed shelf. I would take it a bit hotter than usual as you want it to flow together. I would probably take it to 1480 and hold for 30 min and then take a quick look......
I might change all that if I had it in my hands........really hard to say!
You could also saw it up into lets say 2x2" blocks and use them on another base sort of like pattern bar sort of effect. That could be a cool look. Hmmmmmmm
Why complicate the schedule? 100 dph to process temp and hold as long as it takes.
Please tell me what the 15 minute hold at 300 and the 10 minute hold at 1050(on the way up) accomplishes.
You could slump at 1200 or so, I'm not sure it makes a difference for a shallow plate.
Spectrum may specify that anneal for 1/2" thick glass but I'd go a lot slower.
300 dph to room temp is too fast also.
I'm with Laurie on cutting it up.
I'll cut it up and hope I get something nice out of it. It took me 7 months to get around to slumping it. I imagine it will take me another 7 months to cut it up.
Thanks for the link- I've never looked at them before (I'm a BE user).
I can't imagine using those schedules on any glass- the time saved by changing the ramp up is negligible when you factor in the time to set up the piece and the cost of the glass. What earthly difference does another 6 hours make on the ramp up for a 1" thick piece?
How much heat equalization does a 15 minute hold give at those targets?
For a 1 " anneal I'd hold at 950 for 4 or 5 hours, not 2, and 250 dph from 700 to 100 is asking for trouble.
There's also no discussion of what's going in to the kiln- lots of small pieces? big chunks of previously fired stuff? It makes a huge difference.
I'm sure that people have gotten glass whole out of their kilns with schedules like that but I sure wouldn't want to put money on the long term success of the work.
i'm sure there will be some one who will say not to ,,but why not try and refuse this . turn it over put dams around it ,,if you can line it up ,i see one corner has really slumped ,,but still it may be worth looking at ,that way you will have a nice flat slab to do some thing with,,i have done this with a blank i tried to slump and made a mess of. it did work
