Saturday, February 22, 2014

I see said the blind man…

I my last post I spent a fair amount of time licking my wounds do to a massive air bubble that formed under a piece I was firing.   I was fairly confident I could fix things by doing another tack fuse.

Well it worked…sort of.

The bubble fused flat and there’s a hole where a check of glass broke off.  Not a big deal since that will be filled in with frit.


The point where I got hammered was the cool down after the anneal soak. After the piece had been out of the kiln for about a day a crack formed along the boundary of the pot melt.




I spent a couple of days scratching my head of over this one before I realized what the problem was.  I used a cool down schedule which I though was appropriate for a piece that had an overall thickness of ~9 millimeters.  the problem was my piece was not uniformly 9 millimeters.  Here’s the cool down portion of my schedule.

Ramp Target Hold (in minutes)
FULL 960 80
75 800 0
150 700 0
200 100 0

I think this would have been OK if the piece was uniformly 9 mm thick but this was too aggressive relative to what I was trying to do. 3mm glass is going to cool much faster than 9 mm and that’s what introduced stress along the boundary of the pot melt.  If anything I need treat as though I were cooling down something that was 12 – 15 mm thick due to the varying glass thicknesses.  Here is the schedule I plan on using next time.

Ramp Target Hold (in minutes)
FULL 960 100
50 800 30
75 700 30
100 100 0

I’m thinking (knock on wood) this should do the trick.

I’ll keep ya posted.

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