Hi-Fire Question

[Heidi]

I've made a 10" round hi-fire piece about 3/8" thick, BE glass. For the dam I cut out a circle in a piece of Ceramaguard and lined it with fiber paper.

I now want to refire it without dams to let it spread out to 1/4" thick with natural edges. (On a 21" round shelf, plenty of room, right?)

First firing schedule: AFAP to 1700 hold 60, AFAP to 1000 hold 30, AFAP to 960 hold 2 hours, 50dph to 750 shut off & cool to room temp.

My questions are how fast should I ramp up when I refire and what temp will it take to flow out nicely. Should I hold at 1500 until I like it or go up to 1700 and hold until I like it? Will the glass move differently at the higher temp?

I know my anneal schedule seems like overkill, but I wasn't sure how thick this would end up being and I wanted to be sure.

Thanks for your help,
Heidi

[Amy Schleif-Mohr]

Heidi,
I wouldn't go back up to 1700 for several reasons. First, the more you high fire a piece the more likely the different glasses involoved will become incompatable. Second, you will achieve the same result at a much lower temperature and you won't risk out of control glass flow. If you want the glass to flow I would put dams up on the edges of your shelves so that if the glass does flow to the edge of the shelf it will be caught and you'll avoid a potentially serious problem.

Amy

[Cynthia]

My questions are how fast should I ramp up when I refire and what temp will it take to flow out nicely. Should I hold at 1500 until I like it or go up to 1700 and hold until I like it? Will the glass move differently at the higher temp?

I know my anneal schedule seems like overkill, but I wasn't sure how thick this would end up being and I wanted to be sure.

Thanks for your help,
Heidi

This is just a guideline and is for a top firing kiln. If you have side elements you may want to baffle and make adjustments to fit how your kiln fires and to fit your comfort level.

For a piece that is 3/8" thick I would ramp up at 350 to 1500 and soak 'til you get the flow you want. Use an overglaze or flux to prevent devit. then afap to 960 and if 1/4" thick, hold for 20 minutes. Then 100 dph to 870, then 200 dph to 750 then off. For fewer stages, hold for 30 minutes at 960 then ramp down at 150 dph to 750. If you are concerned that this is too fast, increase your hold to 45 minutes, but 150 to 700 would be fine.

[Heidi]

Heidi,
I wouldn't go back up to 1700 for several reasons. First, the more you high fire a piece the more likely the different glasses involoved will become incompatable. Second, you will achieve the same result at a much lower temperature and you won't risk out of control glass flow. If you want the glass to flow I would put dams up on the edges of your shelves so that if the glass does flow to the edge of the shelf it will be caught and you'll avoid a potentially serious problem.

Amy

Amy,

I suspected the lower temp would be better but I wanted to hear it from someone with experience.

I will dam at the edges for safety. I'm looking forward to seeing how much this spreads.

Thanks for responding,
Heidi

[Heidi]

Thank you Cynthia. That schedule looks good and helps me a lot.

I've been cheering you on for your big show. I'm secretly admiring your courage and am sure you'll be rewarded tenfold for taking on the challenge.

Heidi

[charlie]

I will dam at the edges for safety. I'm looking forward to seeing how much this spreads.

Thanks for responding,
Heidi

in a perfect world and if it flattens out to a perfect 1/4" thickness, it should be 12.24" in diameter.

the math is left as an exercise to the reader.

[Heidi]

in a perfect world and if it flattens out to a perfect 1/4" thickness, it should be 12.24" in diameter.

the math is left as an exercise to the reader.

Thank you Charlie. I plan to watch it when it reaches temp, but I'll be less concerned about too much spreading thanks to your estimate.

However, I will measure the finished piece and report back.

Heidi

[chuck666]

In regards to the first firing, does everyone that has done open casting go to 1700? What do you gain by going so high? If you went to say 1500 for 2 hours, wouldn't the piece look the same?

Chuck