Larry Phillips on tue 19 jun 01
What would the effect of an overfiring (to cone 11 or 12) be with
respect to the ash already deposited at a lower temperature?
The reason I ask is that I got a few pieces back that had virtually no
'ash blush', and a large number of other pieces in the same firing were
similarly devoid of blush. In my case, the pieces had been thinly
brushed with Helmar slip, and a lot of the other pieces were, too. I was
quite surprised to see the lack of action, as Helmar slip has always
shown a lot.
Could the overfiring have burned out the ash colouration?
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Larry Phillips on wed 20 jun 01
dan mickey wrote:
> Also was the kiln salted?
No.
> What is the recipe your using with helmar? what type of clay
> are you using? and what type of kiln was it fired it?
Not sure about the recipe. It was supplied by the club. I used ^10
B-Mix.
The kiln is a downdraft we built a few years ago. It has a top made from
kiln shelves covered with a refractive blanket. It's had some very nice
results.
> It could also be , although very unlikely, that the kiln was more
> oxidized than reduced, and if the slips and clay are not set up for this
> then the results will suffer.
We tried to keep it tin reduction for the latter part of the firing.
> If the work seems really dry, or has little color development, then
> it may be that it was fired to quickly.
This might be it. It was started at about 7AM, reached ^08 at about
11:30. ^10 was down at 14:30.
> hope this helps.
It does, Shane. Thanks for the comments.
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dan mickey on wed 20 jun 01
larry,
Ash blushing or flashing does not burn out. This is not the type of effect
that is erased with high temperatures. A large majority of woodkilns are
fired to ^12+ all the time with flashing intack. The culprit is either in
the kiln or your slip or clay. Also was the kiln salted? salting a woodkiln
tends to lower the flashing because the volitized salt sticks all over the
piece, whereas unsalted woodfired work tends to be "drier" on its backside
thus flashing. What is the recipe your using with helmar? what type of clay
are you using? and what type of kiln was it fired it? The variables are
endless. It could also be , although very unlikely, that the kiln was more
oxidized than reduced, and if the slips and clay are not set up for this
then the results will suffer. Look at rock creek pottery's pots and then
compare them to people who use their recipes, see they fire nuetral to
oxidation, the difference is visable. If the work seems really dry, or has
little color development, then it may be that it was fired to quickly. If it
is dry, try adding a little silica and a little more flux to your slip this
will lower the temp of the slip a little and make flashing more likely to
occur. hope this helps.
shane mickey
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