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flipping for a second firing
Submitted by baxters on Thu, 07/01/2010 - 00:29.
I have fused a 14.5" diameter strip bar (White) with a pattern bar section running through it. It is 3/8" thick . Firing schedule was:
300/1000/15
400/1250/30
450/1500/60
9999/960/2 hrs
100/500/00
Due to the steel dam and fiber paper I have spikes around the edges and on the top towards the center there is a tiny dip-1/16" slightly below the top surface. I think I should flip it to the(bottom side up) and refire to even out the surface and round the edges. My questions are:
1. Do I dam it again? If I do the edges will not round? Is it too thick to fire w/o a dam?
2.What should my firing schedule be?? The same? Longer soak at a lower temperature? Shorter soak @ lower temperature?
I have never done this (obviously) I really don't understand how do this. I have heard of this being done but no details.
I will cold work the piece, sandblast and slump(possibly) Any help would be appreciated!
By the way, I love my homemade strip cutter!
Thanks
Susanne
Hi Susanne, First, you can
Hi Susanne,
First, you can avoid this in the future by cutting your fiber strips (used for dams) 1/8" shorter than the final thickness of the piece. When you do this, surface tension will give you a nice, rounded edge.
Second, in your firing schedule above, I would replace this:
450/1500/60
with this:
9999/1500/60
There is no real benefit to slowing down between the squeeze at 1250 and the full fuse at 1500. In fact, the slower heating in this range may contribute to increased devitrification.
If you are going to grind the spikes and simply fire polish, you can likely do it without dams. If you are going to repeat a full fuse (with a hold at fusing temp) then you will need to re-dam the piece.
The biggest change you will need to make on the re-fire is to reduce your initial ramp to avoid thermal shocking the thicker piece. It is very kiln dependent - but as a rule, I refire 3/8" pieces at 100F/hr. That may be overly conservative - but I can't remember the last time I broke a piece :-)
Paul
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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com
Do you think I need to soak
Do you think I need to soak at 1250? I was hoping to flip it and refire w/o a dam and w/o a soak at 1500. Is this a possibility?
Thanks for your help.
fire polish or leveling of surface
My understanding was that you wanted to get rid of a dip in the surface. What you are proposing now is very similar - although higher in temperature - to fire polishing. If you want to level the surface, you need to give the glass time and heat to move. This requires a longer soak at the forming temperatures. Yes you can eliminate the bubble squeeze.
Stephen Richard
blogs at: http://www.verrier-glass.blogspot.com/ and http://www.glasstips.blogspot.com/