firing schedule drop out
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carol nahoom
- Posts: 17
- Joined: Mon Nov 03, 2003 8:12 am
- Location: Crawfordville, Florida
firing schedule drop out
I am firing a 7" square with a 3" square drop out using 1" Duraboard. The Bullseye is 2 layers cut to 6 3/4". I am using 1" posts so it is dropping 2". For a 3" center drop out should I hold at a lower temperature or take it to a higher temperature? Does the smaller size of the drop out require whether to take it to a higher or lower holding temperature? I have been going to 1350 and holding it for 45 minutes. I know that, usually,slumping is usually done at a much lower temperature but with the smaller opening I didn't know what I needed to adjust. I am firing 3 pieces at one time and cannot seem to find a happy medium for all three. Some are slumping more and some less. I know where my hot spots are in the kiln and have been avoiding that area when I slump. I have checked the archive but couldn't find an answer to my question. Any suggestions will be greatly appreciated. Carol
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Bob
- Posts: 215
- Joined: Mon Mar 10, 2003 1:01 pm
- Location: Salt Spring Island, British Columbia
- Contact:
Hi Carol
The temperature at which slumping occurs is a function of the diameter of the hole that the glass is slumping through. The wider the hole the lower the temperature at which slumping occurs. Each size of drop through mold will have different slumping characteristics. Try heating your piece up at 300F per hour until it just starts to bend ( ~1100F for large molds, > 1200 for small molds). Hold it there for 30 minutes to determine how fast it is slumping. Increase the temperature 25Fdeg and hold it again. Keep increasing the temperature in increments of 25F (followed by a hold) until the piece has slumped, or until the piece is slumping at a reasonable rate. If you want straight sided pieces (upside down top hat) increase the temperature rapidly. If you want shallow sided pieces (upside down padre's hat) increase the temperature slowly.
If you want pieces to be of similar shape then I would recommend that you only use one size of molds at a time when slumping.
Hope this helps.
Cheers,
Bob
The temperature at which slumping occurs is a function of the diameter of the hole that the glass is slumping through. The wider the hole the lower the temperature at which slumping occurs. Each size of drop through mold will have different slumping characteristics. Try heating your piece up at 300F per hour until it just starts to bend ( ~1100F for large molds, > 1200 for small molds). Hold it there for 30 minutes to determine how fast it is slumping. Increase the temperature 25Fdeg and hold it again. Keep increasing the temperature in increments of 25F (followed by a hold) until the piece has slumped, or until the piece is slumping at a reasonable rate. If you want straight sided pieces (upside down top hat) increase the temperature rapidly. If you want shallow sided pieces (upside down padre's hat) increase the temperature slowly.
If you want pieces to be of similar shape then I would recommend that you only use one size of molds at a time when slumping.
Hope this helps.
Cheers,
Bob
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carol nahoom
- Posts: 17
- Joined: Mon Nov 03, 2003 8:12 am
- Location: Crawfordville, Florida
firing schedule drop out
Bob - thanks for the information!
With the heat difference in the areas of my kiln I am working on firing 3 or 4 at a time and having them all slump about the same - a challenge. I took 3 out this morning and just reloaded it moving the pieces around a little. Two were fine and the other could have gone a little more but still OK. Thank you again.
carol
With the heat difference in the areas of my kiln I am working on firing 3 or 4 at a time and having them all slump about the same - a challenge. I took 3 out this morning and just reloaded it moving the pieces around a little. Two were fine and the other could have gone a little more but still OK. Thank you again.
carol
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Bob
- Posts: 215
- Joined: Mon Mar 10, 2003 1:01 pm
- Location: Salt Spring Island, British Columbia
- Contact:
Carol,
Have you tried the Bullseye test to determine how the heat varies across your kiln? It invovles building small bridges of glass at a regular spacing over the kiln shelf. Fire them until they start to slump. Turn the kiln off. Once the kiln has cooled check the bridges to see how much difference in slumping there has been across the kiln. Although it is not quantitative it will give you a general idea of the differences. This could be quite important for larger pieces.
If there is a big difference try Brian's Baffle-n-go technology. Place cut up pieces of shelf to loosely cover the elements around the inside perimeter of the kiln. The heat will radiate from the baffles and hopefully even out the heat distribution. (Is that how it works Brian?)
Cheers,
Bob
Have you tried the Bullseye test to determine how the heat varies across your kiln? It invovles building small bridges of glass at a regular spacing over the kiln shelf. Fire them until they start to slump. Turn the kiln off. Once the kiln has cooled check the bridges to see how much difference in slumping there has been across the kiln. Although it is not quantitative it will give you a general idea of the differences. This could be quite important for larger pieces.
If there is a big difference try Brian's Baffle-n-go technology. Place cut up pieces of shelf to loosely cover the elements around the inside perimeter of the kiln. The heat will radiate from the baffles and hopefully even out the heat distribution. (Is that how it works Brian?)
Cheers,
Bob