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Glaze Ghosting on Shelves


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#1 nairda

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Posted 20 September 2012 - 09:50 AM

After glaze firings (Cone 6, electric) 'ghost' rings of some pots show up on the kiln shelves. I typically keep firing on the shelves until the rings become quite numerous and then I add more kiln wash to cover them.

  • Since the rings don't form around every pot, is this the result of 'powdery' glazes sort of misting off during the firing?
  • While pots don't seem to stick when set on top of a 'ghost ring', do I really need to be adding more kiln wash? My kiln wash is 25% calcined EPK, 25% EPK and 50% Alumina Hydrate and it holds up really well otherwise.
Searched the forum to see if this had been addressed in the past but didn't see anything. Thanks.

#2 neilestrick

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Posted 20 September 2012 - 10:04 AM

It's not the glaze dusting off. It's fuming. Some glaze materials and oxides, like copper and cobalt, will fume out a bit during the firing, and the kiln wash takes it in. It won't hurt anything, as it's not enough to cause other pots to stick or anything. I used to take advantage of it in the wood kiln by tumble stacking pots covered with copper slip right next to pots with shino. The shino would take in the copper fumes and go earthy pink/purple/blue/green. Fun stuff. Tom Coleman used to do it in the gas kiln to produce copper red blushes on his white and celadon pots.
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#3 JBaymore

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Posted 20 September 2012 - 10:16 AM

Unless you are having really significant "disasters"... that kiln wash recipe you are using is a pretty expensive mix. Alumina hydrate is expensive compared to silica and stuff like EPK. Likely is it "over-kill" for most uses. You might save yourself some money by, at the MOST, using 1/3, 1/3, and 1/3. Likely a 50 / 50 of EPK and silica would do you with no alumina hydrate.

best,

.............john
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#4 nairda

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Posted 20 September 2012 - 07:50 PM

Unless you are having really significant "disasters"... that kiln wash recipe you are using is a pretty expensive mix. Alumina hydrate is expensive compared to silica and stuff like EPK. Likely is it "over-kill" for most uses. You might save yourself some money by, at the MOST, using 1/3, 1/3, and 1/3. Likely a 50 / 50 of EPK and silica would do you with no alumina hydrate.

best,

.............john



#5 nairda

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Posted 20 September 2012 - 07:51 PM

Thanks John and Neil.




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