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Author Topic: I need a bit of advice on kilns  (Read 1929 times)
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Jules1971
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« on: November 09, 2016, 02:45:41 PM »

Hi Everybody,

im new to this sort of thing but my main interest is slumping and forming new things out of bottles and glass.
but my main question that im pondering is:

Would a gas fired kiln be suitable for slumping the reason i ask this is that im a gas engineer by trade and do this for a living running my business.
so i would ideally like to build my own kiln so i have more control over the size and accessibility inside.

i will more than likely move onto making all sorts of stuff in the future but at the moment i just want to do slumping to gain confidence and move on from there

any advice would be greatly appreciated.

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Zeldazog
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« Reply #1 on: November 09, 2016, 03:29:12 PM »

From my knowledge of kilns, and gas kilns for ceramics, I can see no reason, theoretically, why you couldn't use a gas fired kiln.  The reduction process isn't normally used in glass fusing and slumping (I've only heard mention of reducing flames for lamp-worked glass), but of course gas kilns don't have to be, and are not always, reducing.

However, firing glass involves long and extended firings, and one of the most important aspects of glass fusing & slumping is the controlled cool down and anneal soak.

From memory, when we fired the gas kilns at Uni, we never left the gas kilns unattended - until it had finished heating, then the gas was switched off and the kiln allowed to cool down naturally.  With glass, you have a controlled cool down to ensure that stress is removed and not re-introduced in to the glass.  The larger or thicker the piece, the more important this section is, and the longer it has to be.

The ability to control that firing program is an important aspect of fusing and slumping glass - do gas kilns have as much control with ramps and holds (a typical ceramics firing, two ramps and one soak at top temperature, a typical glass firing, is ramp, hold, ramp, hold, ramp, hold, rapid cool down, hold, slow cool down - ish!)?  Can that be done with a controller, or would it have to be manually?  And are you happy to leave a gas kiln unattended?  It's really about whether you are able to be around for a 12 to 17 hour firing schedule, although as a gas engineer you may be happy to leave your own product unwatched  Grin

The other point to make about the other main difference between dedicated glass kilns and others is that the ideal design is a single shelf/flat bed with heating elements across the top - this gives a very even firing across the span of a piece.  Whilst it is true that glass can and often is fired in ceramic kilns (I cut my teeth fusing in ceramics kiln for over a year), there are issues - side heating can cause the edges to fuse before the middle, creating issues with trapped air and bubbles, etc

I've no reason to think that technically, glass cannot be fired in a gas kiln, but I don't know enough about gas firing kilns to know whether they have the same flexibility of control.







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Moira HFG
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« Reply #2 on: November 09, 2016, 06:02:20 PM »

I have a feeling that someone told me gas kilns are pretty good for glass, because the temperature is stable and controllable. I thought it might be Stephen Richard - but this is all I can find on his blog:

http://glasstips.blogspot.co.uk/search?q=gas+kiln

His blog is worth reading anyway, lots of good tips!

As Zeldazog says, the key to success is accurately controlling temperature through the different stages of the heating/cooling/annealing process. I daresay there is kit available for this - some sort of timer/thermostat combo.

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babyshoes
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« Reply #3 on: November 10, 2016, 03:47:02 AM »

From my limited research into bead annealing kilns, it seems that the controller is the expensive bit. I think you can buy them separately, so theoretically I see no reason why you couldn't make a home made gas kiln work with the right controller.
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Lee - Kilncare
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« Reply #4 on: November 10, 2016, 05:17:05 AM »

Excellent reply Zelda as always.
Gas kilns are good for glass but their real advantage is the speed that you can get them up and down. Brilliant for multi firings per day.

However, gas kilns can be vicious. A gas kiln that will give a steady controlled heat for the critical annealing process is something that you cannot simply guess at.

The other downside to a gas, glass kiln is that it is not a stable atmosphere. Electric kilns have a relatively stable atmosphere with respects to air movement, or lack of it. The basic principles of a gas kiln is that they heat the kiln by air movement, forcing in the jets of hot gas/oxygen into the chamber to create the heat. This in turn does run the risk of forcing any lose particles to become air born and possibly land on the glass surface.
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Zeldazog
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« Reply #5 on: November 10, 2016, 01:51:18 PM »

Excellent reply Zelda as always.

The other downside to a gas, glass kiln is that it is not a stable atmosphere. Electric kilns have a relatively stable atmosphere with respects to air movement, or lack of it. The basic principles of a gas kiln is that they heat the kiln by air movement, forcing in the jets of hot gas/oxygen into the chamber to create the heat. This in turn does run the risk of forcing any lose particles to become air born and possibly land on the glass surface.

Thanks, Lee.

I did wonder about that bit too, but don't know enough about gas kilns to guess.
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Jules1971
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« Reply #6 on: November 10, 2016, 05:28:17 PM »

thanks Everybody the replies are amazing in the knowledge you have i really am grateful it has given me food for for thought and my thoughts for design etc.

if have anyone has anymore thoughts it would be greatly appreciated.
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