Sour Dough Clay

We try to allow ourselves a little time ‘off’ over the summer from the usual on-going procession of jobs. This year we had two lots of relatives visiting, so that was a good excuse to not do any other work for a week or two. Then I taught a Master Class in fine throwing and turning techniques up in Sydney for a week. So now it’s back to work. The very real work of essential property maintenance and more clay making while the weather is hot.

I have been spending time over the summer to prepare ‘clay’ for the coming year. When I say ‘clay’, what I mean by ‘clay’ and what other potters understand from that term are completely different things. I have been crushing and grinding my local porcelain stone down to a fine powder and then ball milling it into a fine impalpable stone paste with a little bentonite to make my native bai-tunze porcelain body. It isn’t plastic and sticky like most potters clay. This wet rock dust is just that. Wet rock dust. It needs a long time weathering and souring to develop any sense of cohesiveness and plasticity. The 15% of illite clay mineral that is present in the stone, gives it some similarities to the weathered ’sericite’ mica bodies of the orient. Illite is closely linked to fine weathered mica minerals, so it does give it some plastic qualities after a few years of ageing.
I’m constantly trying new ways to see if I can improve the workability of my local stone somewhat, but there isn’t much that you can do with non-plastic rock dust. Other than to add some kaolin and bentonite, which is what I already do and what I saw them doing in the porcelain clay factory in Arita.
Same problem, same solution!
This last year I experimented with another approach to plasticising my rock dust. This time last year, I set aside one 50 litre batch of ball milled porcelain stone slip, and instead of stiffening it on the drying bed, then setting it aside to ‘age’ in a plastic state. I have tried to leave it to settle, flocculate and ‘age’ in the slip state. This produced a very interesting result. The slip developed some sort of ’skin’ on its surface, but below the clear water that appeared above the slip as it settled. This ‘growth’ of skin must be some sort of living material like algae or something similar? I’ve never seen anything like it before. It was quite strong, as I was able to depress a bulge down into it to get the bucket into the barrel to drain off the water from the top. The skin didn’t break and allowed me to recover all the surface water without disturbing the clay below. It even held together well as I lifted it up off the surface of the slip underneath. There was some greenish algae-like growth around the edges of the bucket, where light could get in. This isn’t unusual, as I get loads of green algal-like growth in my clay bags that are set aside to ‘age’. I make my bodies from natural stone powders that I grind myself and I use mostly naturally acidic tannin infused water from the water tanks connected to the pottery roof. Tannin is well documented to be beneficial to plasticising clay materials, as is maintaining an acid pH to counter the natural release of alkalis from the broken down stone fragments as they are ball milled. The overall effect of these natural ingredients is that there is no chlorinated water used in its production and no sterilisation of the powders or any heat treatment of any kind, so the clay is still alive with whatever organics there where in it in the first place.
I’ve kept the ’skin’ to investigate further. I may be able to use it like a sour-dough starter to inoculate the next experimental batch of porcelain body?
When I started to mix the settled and aged slip, it was very viscous and then when I poured it out onto the drying bed and scraped out the bucket, my fingers started to stick together with the extreme viscosity of the slip. I haven’t felt anything quite like this from porcelain slip before. I once had a bucket of porcelain glaze that I kept for special purposes, and then didn’t use for a few years. When I open the bucket and stirred it up. It had set to a stiff gel and took a bit of effort to stir. My fingers stuck together with the viscosity of the glaze at this time too. Ageing has this plasticising effect and is a good thing to do if you can afford the time. I’m 64, so I don’t have a lot of time to do these kinds of experiments over the very long term. I’m keen to see how this specially aged liquid slip batch of porcelain body develops and throws this time next year.
Only time will tell.
Summer is also a time of fresh garden salads and veggie BBQs. We have a lot of tomatoes, zucchini, aubergines and basil at the moment, so every meal is some sort of variation on ratatouille. Baked, poached, pan-fried, BBQ’d and/or grilled. I’m trying to keep it varied and interesting in lots of different ways.


Best wishes from all-natural, sour-dough, clay-boy