Glazing is well underway and I'm preparing the last of the rocks needed for my rock glazes - a coarse pink granite and a darker microgranite from Cumbria. I've crushed and milled the hardest/most difficult rocks - notably a Cumbrian rhyolite and some of the limestones I have - and these last are pretty easy.
First up I calcine them in my small test kiln - just up to a good red heat - maybe around 800C. It doesn't matter exactly how hot as long as the rocks are red hot right through. Sometimes I have to use a steel mallet to get them into manageable size and they are truly hard! These have been calcined + all the moss/lichen burnt off.
During this process the crystals in the rock expand and contract at different rates making them beautifully crumbly. Next it's the turn of my trusty mortar and pestle, and a good stretch of time.
Repeated crushing and seiving
to get the rocks down to this size grit. They are then dry ball milled for 3 hours or so to get the particles down to dust size, which is probably around 100 - 120 mesh.
Then, blending with other rocks and clays to get my glazes. I'm aiming to finish glazing this coming week, finish splitting wood and still have to grind glazes off the floor of the kiln.
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