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Smoking Kiln


Pessy
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I had a fully loaded kiln, where I might've used wax resist excessively, and possible started firing before the wax was dry. My smoke alarm went off at 700 degrees, so I stopped the kiln, and unloaded. The wax on all the pieces are burnt, and the shelves appear slightly burnt too. Is this normal? I've never before checked what happens during the firing process. 

If this is ok, can I reload and fire again? Will the results be affected by my stopping the kiln?

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Hi Pessy!

I use wax on almost every piece - to get a sharp boundary/transition at the rim between liner glaze and outside/color glaze - hence a strong odor early in the firing cycle, but not enough to make clouds of smoke.

No doubt the wax (along with glaze ingredients that burn away) is designed to fully burn away; I've not noticed any marking where the wax was, any road. Hence, my guess would be normal on question one.

As for re-firing, I haven't (yet) had the experience of re-starting an interrupted glaze cycle, however, reading indicates yes on question two and no on three.

I'm curious to know if the wax burns more cleanly with an air supply? I've fitted my (also somewhat ancient) Skutt with a kiln vent, which pulls a small stream of air from the bottom of the kiln, hence, small streams of air are pulled in through the various cracks, as well as the small holes drilled in the lid. Kiln venting is recommended for longer element life, more thorough bisque burnout, and nicer glaze colours.

While the kiln vent helps quite a bit with the fumes, I did not feel comfortable being in the studio, at all, during firing, so have also set up an overhead rig to pull heat and fumes; it's noisy, but works well.

Edited by Hulk
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7 hours ago, Pessy said:

If this is ok, can I reload and fire again? Will the results be affected by my stopping the kiln?

Yes it is ought to be just fine. Wax burns off at around 800 degree f so in the range of let’s say 450 degrees to maybe 850 degrees folks often smell the wax. Use a lot of wax, lots of smell. You should not see any signs of carbon as it will burn away in the rest of the firing. Any kiln vent will help this but downdraft vents are often not capable of removing the smell completely …… and they are not really designed to get all the wax smell. So a downdraft will help but not likely to capture all of the wax smell. The smell will however disappear above 800 degrees.

As far as refiring, a simple general way to think of this would be: for a glaze firing, if you have not fired within 300-400 degrees of you finish temperature then you have not done much real heatwork. Silica and alumina don’t melt less than 3000 degrees so they need flux and enough kiln energy  to help them melt earlier. Until your kiln reaches this melting temperature (often called a eutectic) not much is done in the way of useful work on the glaze. So refiring is generally just fine for most. Technically (Per the Orton cone chart) most of the relevant heatwork to maturity is done in the last 200 - 250 degrees of the firing.

For bisque firing, generally it’s not a concern, just rebisque to your proper cone. Generally It’s ok to bisque more than once and often done when multiple layers of decoration are desired.

Edited by Bill Kielb
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