Sunday, 28 February 2016

Glazes: from Stoneware to Midfire

I have been firing to cone 6 (1220o C) ever since my student days. Opening the stoneware firing kiln and  finding my "elegant" (thin) lids warped like frisbee left in a hot car was the deciding moment.
I have tested most of the local stoneware clays and discovered that they are vitrified at cone 6 - so why not? Colours are better, there is less wear and tear on the kiln and less stress for the clay.
But a few months ago I have got a challenge: Lower the firing temperatures for the Belmont Potters Group.
The Group has been talking about it on and off for years, but it could not quite make the decision to "jump" into it.
The biggest stumbling stone: What shall we do with all the Stoneware glazes?
So first thing that we did was to fire all available glazes to the cone 6 (1220oC)

And discovered that they are not very exciting, but there are a few we can keep:

We chose some complimentary glazes from my files (bottom row):

(I have to apologize for the quality of the images. My phone really does not give them justice)
...and mixed them up.

And than comes the exciting part:

By testing each glaze on top and under each glaze (superimposing) we have a complete range of choices:

yes, all of that:

On the closer inspection, the kiln was slightly underfired, so they all went back again, 10 degrees higher.
I'm going to the Belmont Potters now, to see how did the second firing go. And I will take a camera with me.

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