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Hi all ,,Would anyone care to tell me what i am doing wrong. Am using spectrum 96 glass, the blanks were 14 cm wide and 7 mm thick. The first one i tried to slump through a drop ring popped after a few hours after coming out of the kiln the 2nd was in bits when i opened the kiln next morning
175 500 000
200 650 30
200 725 2 hours
asap 482 40
200 100 00
the second one took 3 hours to get nice slumping and i held it at 482 for a full hour to anneal .the walls of the vases are about 1.5 to 2 mm thick at the thinnest ..Am using a Paragon high fire kiln

Paul,

My thoughts are the glass is not properly annealed. The first suggestion would be to slow the ramp down from 482. The soak at 482 is to equalize the temperature. The cooling from 482 has to be slow enough to prevent reintroduction of a temperature difference between the interior and exterior of the glass.

My second suggestion would be to anneal the glass longer both at the soak point and during the ramp. The glass is varying in thickness and that makes annealing more difficult . Also the drop through mould is going to hold heat in it and the release of heat will be different than along the sides. I would anneal for twice the thickness of glass. Check S96 website for their annealing schedules. You've put so much effort into the piece that a bit more annealing time is worth it.

Those are my thoughts.

Cheers,

Bob

also verify that your temps are accurate. r.

(for reference, my My deg c to f conversion is:

347 932
392 1202
392 1337
212 899.6
392 212 )

IMO, you are ramping too fast in all segments, especially if you have a relatively short, top-firing kiln and and the glass is close to the elements.

I would ramp no faster than 150 to 200 deg f/hr. Also, that's a pretty hot drop temp, at least in my kiln, which would result in very thin sides. So you've likely got a thick rim, thin sides, and thick bottom. The uneven thickness will create stress, requiring a longer annealing time. Also, Spectrum anneals at 510/950.

So... lots of factors to consider, but basically, a rework of your firing schedule.

Dana W.

Here is a schedule I have used for a drop vase of a similar size (but not construction -- my colors were a transparent pink and all designs were painted). The glass, however, was Spectrum:

1 150 1100 30
2 100 1250 60 (I would have watched here and lengthened/shortened as necessary)
3 1500 950 120
4 100 700 00

I have a firebrick kiln, so the cooldown to room temp after the kiln shuts off is pretty slow.

Please excuse my use of Fahrenheit -- I copied this out of my excel spreadsheet

Dana W.

Hey thanks ,you guys ,,so i guess all in all slow the whole thing down and anneal twice as long,,,