I was recently in China doing some research. I have written a little bit about that, intermittently, in the last month or so. While I was there, I arranged to get my hands on some new and different sericite samples. These have now just arrived here last week and I have done my first tests with them.
I now have 4 different Chinese sericites to compare.
Although it isn’t immediately obvious from the image above. If you look closely, there are 4 different colours of rock samples from top to bottom, white, cream, grey and pale buff. They all look more or less white, but they each have various tints or shades of colour to their whiteness. They all do have one big thing in common. They all throw badly, the palest ones being the least plastic and most difficult. They feel a lot like my local Mittagong porcelain stone, only better behaved.
I felt like I’d gone all the way around the world and come home again when I threw these tests. They felt so familiar.
I’m really looking forward to seeing the results fired. I had a bit of trouble with the usual shrinkage and drying cracking problems, but I did get some of them through successfully. But I lost quite a few. Still, nothing that I’m not used to, and I’m getting good at recycling the turnings and failures.
I almost filled the tray on my old wooden kick wheel with turnings after trimming just 12 small bowls. I must be removing at least half of the weight of the original material to get them thin enough to look and feel like porcelain. I aim for 2mm at the rim and 3 mm lower down, graduating 5mm at the foot. This tapered wall thickness allows the best translucency at the rim and higher up the pot, while retaining sufficient strength to hold the pot up against gravity while it sits at 1300oC in the kin to develop enough glass in the body to be come translucent.
If I’ve done it right, the whole finished, fired, ceramic mass, has the correct quantity of primary and secondary mullite crystals to glue it all together, while becoming glassy enough to allow plenty of light to pass through.
Too glassy and/or too thin and it slumps. Too thick or not fired high enough and it stands up straight, but isn’t very translucent. It’s a bit of a fine line to tread.
As I sit and grind away at this damp, ground-up rock dust with my tungsten carbide tools, I realise that I’m truely happy doing just this. There is a gusty wind outside, but I’m in here sitting in the sun and I don’t want for anything more at this moment. This is fun. I can’t wait to get them into the kiln.
It has all the promise of something special about to happen.
I love that.