Autumn Downey on wed 30 aug 00
Hello Ron and everyone else who has replied,
Thanks for your input. It gives me a better idea of what happened in the
kiln - and Merrilee Pascaris sent me your revision of the glaze, so will be
trying it right away. Will keep an eye of consistency too, because of the
application thickness problems people have mentioned.
Usually we don't get blisters, but on thinking this kiln load over, one
side of the top half was devoted to tall pieces and the side was half
shelves of floating blue pieces. It was the very top shelf that was
problematic.
There would have been more elements heating the area over all, so it may
have actually got hotter but cooled more quickly with fewer shelves to hold
the heat, plus the downdraft to the vent system. (We fired at cone 5, but
the bottom is usually cone 6 and the top around one 4). We live with it
because it actually suits our glaze range.
It seems to me that the original floating blue is almost a cone 4 glaze -
providing it doesn't cool too quickly.
Thank you, Jonathan for pinpointing the oxides that don't do well together.
Another glaze we had that blistered also had those oxides and was
temperature sensitive.
It will be interesting to watch for changes in glazes when we use our last
bag of GB. Thanks for the warning, Ron.
Autumn Downey
(Yellowknife, NWT)
At 11:28 PM 2000-08-28 -0500, you wrote:
>Hi Autumn,
>
>There are many factors to consider - properly fired bisque, application,
>speed of firing, soak period. Some potters use this glaze and get
>consistent results.
>
>You are right - the alumina is very high and so are the KNaO and Boron so
>they cancel each other out - remember - there is a fair amount of MgO
>present and it is most active from cone 4 to 6 - you could say violent. The
>best way to fire such glazes is to slow the firing enough towards the end
>to give it a chance to heal over.
>
>Make sure you know what cone you are firing to.
>
>Some of the last Gerstley Borate that came on the market was quite
>refractory compared to earlier batches - that would not help your
>situation.
>
>I assume you have found some of my variations - with the GB replaced by
>Frit 3134 - if they don't work send me your firing schedule for both bisque
>and glaze firing and I will make some suggestions.
>
>RR
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