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Chris Campbell

Question About Multiple Firings

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I was reading the previous discussion about re-firing a blistered pot and I wondered how far down the problem went ... thinking you could not just aim the solution at the last problem. The blisters could have nothing to do with the glaze but some random component in the clay that might never happen again??

 

Say you have a pot that has been treated somehow ... be it glaze or a wash of oxide or an input of salt or soda in the previous firing ... and you want to fire it again for whatever reason ... do you always have to take into account what has been done before or are there any ingredients that simply fire away?

 

In a salt or soda firing, isn't the salt or soda still there somewhere on the surface waiting to have an effect on the next thing? :huh:

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The heatwork stacks up if you get anywhere near the maturing temperature of the ceramic elements involved.  If you refire and refire and refire.... the impact of the application of that heat energy is cumulative.  Iga ware (a place just across the mountain from Shigaraki) in Japan is a good example of this concept at highfire and in wood kilns.  Historically the pieces (mainly teawares) were refired until they started to sag and crack and fall apart from pyroplasticity (the wabi-sabi aesthetic).

 

If you refire overglaze enamels to the enamel temperatures (something like Orton cone 016 - 013) the enamels continure to melt and will run more due to gravity and will tend to "thin out" (vaporize into the kiln atmosphere) and heat senstive colors will change.

 

If a defect is from underfiring, then refiring will tend to make it "better".  But if a defect is not from that source.... refiring can tend to make it worse.  If it is something like bloating from the outgassing of particles or materials in a pyroplastic clay body...... refiring usually makes the bloats worse, if the body is gas permeable.... it might make it better...... but this is not usually the case.

 

So in general.... I'd say yes.

 

best,

 

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

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In addition to the changes in the glaze melt, you can also get color changes. Many iron reds (tomato reds) brighten if refired at a lower temperature. Many shino glazes turn to a bright bronze-gold color if refired at low fire temps. Test, test, test.....

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