Wednesday, October 23, 2013

It was a dark and stormy night…

Well not really.  Sorry.  I couldn’t think of any better way of continuing the-saga-of-the-never-ending-pot-melt.  In the previous episode I rambled about some possible reasons the melt had spider web cracking.  Unfortunately this sight greeted me when pulled the piece out of the kiln.


I did more research and found that spider web thermal shock can be caused by the glass sticking to the kiln wash introducing stress laterally in the piece while it was flattening out.  It wounded plausible to me since I found bits of kiln wash stick to the bottom of the melt.  So I figured “Third times the charm; I’ll fire it on a piece of fiber paper and give it a bunny firing schedule”.



Well…that didn’t work either. So I opted for Plan B…


So what’s the take-home on this?

  1. I created a piece to thick to begin with which required another firing to flatten.
  2. I made some bad assumptions about how much the piece would thin out and had a cool down schedule that was too aggressive for the thickness of glass.
  3. The kiln wash stuck to the glass bottom introducing stress.
  4. I used orange glass which I have since learned that it’s one of the colors that tends to change COE under extreme heat.
  5. I used some Wissmach glass In the melt and It may not be as well engineered as Bullseye glass and more apt (possibly) to change COE under extreme heat.
  6. I used extreme heat – 1650 degrees.

Now many sites I’ve visited say that the glass needs to be heated to 1700 degrees to get as much it out of the pot as possible.  But I’ve also come across may sites ( included) that recommend 1600 as the max melt temperature.  One of the reasons being that unless you have a ceramic kiln that is designed to heat to 2000+ degrees 1700 degrees is the generally the max for a glass fusing kiln and those temperatures are extremely hard on it.  I also suspect that a lower temp will also minimize any potential COE shift and that a 100 degree hotter kiln won’t really get that much more glass out of the pot.  So I think I’m go with a lower temp with the next melt and see what happens.

So what about all those pretty shards?

Random form Cabochons!


Alight you may be thinking “OK Jones. This is how crazy people roll; doing the same thing over and over again and expecting the same results”.  Well I’m not that crazy (at least that’s what my therapist tells me).  I tried doing a proof of concept in the microwave kiln to see if would get the spider web cracks.


OK.  It does look a bit fugly since one piece of shard toppled over on the bad side but so far I’m not seeing the cracking.  So I’ll fuse a few of them and set them aside for a while to see if they start disintegrating. 

Thus endith this tale for now.

Blogger Labels: Thermal shock,Sorry,kiln,glass,Wissmach,Bullseye,Delphi,Cabochons

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