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Tips, Techniques, and Questions -- Technical questions or tips |
2010-09-24, 1:05pm
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artiegirl
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Join Date: Aug 15, 2010
Location: Cheyenne Wyoming
Posts: 105
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cracked beads
Ok I need some help here
All of a sudden my beads are cracking in half (the entire batch),
I have not changed a thing kiln, torch, glass. what am I doing
to cause this?
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2010-09-24, 1:09pm
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honorary bead lady
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Join Date: Jan 14, 2008
Location: Mostly the doghouse
Posts: 5,180
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Annealed/or not? Large/small? Encased/not encased? Brands? COE?
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2010-09-24, 3:47pm
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artiegirl
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Join Date: Aug 15, 2010
Location: Cheyenne Wyoming
Posts: 105
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Annealed, small and med, encased with clear vetro and cim 104 coe and pastel 104 coe
have any ideas would appreciate it
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2010-09-24, 3:54pm
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Glass Hive Kiln Tech.
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Join Date: Jun 23, 2007
Location: Toledo, OR
Posts: 907
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Well, a crack straight through is thermal. Some where it is cooling too quickly. Is the kiln program the same? With the seasons changing, perhaps the lighting in your studio is leading you to believe it is hotter than it really is before you are putting them away?
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2010-09-24, 4:01pm
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artiegirl
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Join Date: Aug 15, 2010
Location: Cheyenne Wyoming
Posts: 105
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i have a jenken and it is set for the sm and med beads, i let them cook for atleast 2hours the program on the kiln is set for 4 hours of cooking on the 980 degree ( i think its 980) and then after the 4 hours it cools slowly but i have been just turning it off after the last bead is is for atleast 30 min, should i stop doing that?
thank you
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2010-09-25, 5:53am
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Lampworkaholic!
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Join Date: Apr 22, 2008
Location: Cornelius, NC - because weather
Posts: 5,158
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Try ramping down slowly and see if that helps. Hold it for at least 30 minutes at 840, the strain point.
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2010-09-25, 6:10am
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Senior Member
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Join Date: Jun 15, 2005
Posts: 2,251
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If you are turning your kiln off without ramping it down slowly, then your beads are more than likely not annealed. Annealing is the slow cooling of glass down to room temperature to relieve the stress. Holding it for any period of time and then turning off your kiln is essentially not annealing. Thermodynamics tells you that any heat source when turned off will cool fastest the farther away from room temperature it is. So, your kiln may cool a hundred degrees in the first five minutes after you turn off your kiln and maybe another hundred degrees in the next 10 minutes. Glass should be cooled very slowly until it is below the strain point, like 100 degrees an hour. After that you can cool faster, but there can still be cracking due to thermal shock. It's best to cool slowly until you reach 500 degrees. I always cool at 100 degrees an hour until the temperature is 300 degrees and then turn the kiln off.
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