Firing Schedule Produces Spikes


I am a beginning glass fuser. I recently purchased a kiln. I’m full-fusing pendants.

Each firing schedule I’ve used has caused spikes. My kiln is a new Paragon Fusion7. I have talked to the company and also others experienced in the field of glass fusing.

I get all types of tips but unfortunately they all have failed. Some say it is due to…

  • using firing paper,
  • new kiln,
  • faulty kiln,
  • too high a temperature,
  • too long a holding temperature…

With my last try I ramped at 1000F/555C degrees in an hour and targeted 1000F/537C degrees in the first step. I then ramped at 600F/333C and held for about 15 minutes around 1200F/649C. I ramped at 300F/166C to a final heating of 1425F/773. Then I’ve been holding it there for about 25 to 30 minutes.

I never can tell whether it is completely fused when I look through the window. Some say it takes experience and after a while I’ll know when it has completed. After doing an AFAP to 960F/515C and hold for 1 hour, I unplug it. I wait at least twelve hours before opening my kiln once done.

What do you suggest I do? I ground a few of the spikes and then did a polish fire on one batch. It turned out nice. I don’t plan on having to do this each time I use my glass kiln to fuse glass.

Milly’s answer:
Thanks for your question. I think your kiln firing schedule is to blame. Your ramp up is too fast at the beginning and too slow at the end for a top temperature of 1425F/773C.

Don’t panic at this stage about your kiln being faulty – I’m sure it’s not that. It takes a while and lots of tests to become confident with a new kiln and controller – I had exactly the same panic as you with my new kiln!

Firing schedules are complicated. It may be helpful to read my Firing Schedule page to understand what happens to your glass during a firing. Once you’ve got the hang of that, you’ll know all the different factors you have to think of – for example, you don’t tell me what type of glass you’re using – I’d guess Bullseye from your kiln firing schedule? – what the size or thickness of your glass is (one layer or small work is more likely to produce the spikes you’re talking about), or whether your elements are at the top or in the side of your Paragon kiln? Are the shapes solid, or do they have lots of jagged edges? Is it hotter in one place than another? You can probably see by now why I don’t like giving out firing schedules to individuals!

However…try the following programme as a starting guide only – you’ll probably have to adjust the top temperature gradually – up or down by 15degreesF/5degreesC at a time until you build up a bank of knowledge about your particular kiln. You might need to review the ‘hold’ time and the rate of ascent too. Write everything down!

Assuming two layers of eighth inch/3mm Bullseye glass, 12″diameter piece, elements in top, side and door:

400F/222C to 1250F/677C Hold for 30mins
600F/333C to 1480F/804C Hold for 10mins
AFAP to 960F/516C Hold for 30mins
150F/83C to 700F/371C No hold
AFAP to 70F/21C

Open and hopefully be amazed!

I hope that helps. It would be great if you could return with your comments on this page, so that others can see how you got on.



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