Let the Clay Lead the Way – Part Two

So, with classes starting again this autumn, the ceramics research continues. As you will have seen if you read my first post about ceramics, there was clay under the ground where I grew up in Lincolnshire. Well, there was also clay under the ground where my parents lived in Oxford, and there is clay under the ground where I live now. So I decided to investigate whether there is any difference between them.

These delightful looking samples, left to right, are from Boston, Banbury and Botley in Oxford. The sample from Botley is much more refined than the others. I spent large amounts of summer 2015 investigating the clay from Botley, and I washed out a lot of the rocks and sand from some lumps that were dug up when the new owners of my parent’s house built an extension.

As you can see even in their raw forms there are colour differences between them.

In the pottery studio I set about dissolving the clay and washing out the stones from the Boston and Banbury samples. This mostly involves just breaking the clay up into lots of water and trying to dissolve it into a thin mixture. It can then be sieved and left to settle. This doesn’t take long and the excess water can be drawn off, leaving liquid clay or slip.

Of course these “garden slips” are not going to be pure clay, even with the large stones, sand and organic matter washed out. But they do represent both a historical element from different phases of my life, as well as very different eras of natural history. For example, back in the 80’s when I was experimenting with refining clay where I lived in the centre of Boston, there would be many seashell fragments even though where I was digging was about seven miles from the sea. In 2015 when I refined the Botley clay there were coral and fossil fragments in it, and Botley is many, many miles from the sea. So it is interesting that in digging down only a matter of feet we can possibly travel back in time hundreds, maybe thousands of years (bearing in mind I am just guessing here, I’m not an archeologist). The years of my own life are put into perspective in those terms, even if the distances between where I have lived remain relevant.

Once I had slips for all three samples I prepared small stoneware tiles to test them on.

Slip needs to go on wet clay, and the classes I attend use a buff clay as standard. As you can see we have, left-to-right, Boston, Banbury and Botley, and a control piece. There are clear, if subtle variances between the slips in their wet forms.

The classes have weekly bisque and glaze firing schedules; these samples have to be bisque fired first which gets all the water out of the clay and makes it hard; bisque fired clay is unglazed, but will not dissolve in water any more. The buff clay goes from grey to pink on the bisque firing.

After bisque firing the results were interesting;

As you can see, the darkest clay in raw form (Boston) turned out the lightest, and the lightest (Botley) turned out the darkest. These have now been half-glazed to see what the hotter glaze firing does. The buff clay becomes yellow-ochre in colour in the glaze firing.

Note how the garden clay melted at the high temperature needed for glaze firing

In the past my experiments with “garden” clays have been interesting. Back in October 2016 we test-fired the clay from Botley in the kiln at different temperatures. My tutor advised me to make saggars (little clay boxes) for the samples. I did not believe him when he told me the clay would melt at high temperatures but sure enough whilst it turned a beautiful cherry red at 1040 degrees Celsius (Cone 5), it totally melted at the higher glaze temperature of 1245 degrees Celsius (Cone 6) Had it not been in the saggar, the kiln may well have got messed up.

With these properties in mind, using these garden clays as decorative slips has resulted in some very random effects, from being almost hidden under glazes to bubbling and melting beneath them and causing strange effects on the surface. The glazed examples are currently awaiting firing so we shall have to see how they turn out – check back here for the results!

In the meantime, work on more test pieces continued, including pierced circular and scratched forms and larger circular pieces. The motif of a circle in a square has been something I have explored in painting for years. I’ll have to explain it some day.


Meanwhile down in the garden, I did my own firing experiments with Botley clay in my incinerator. More on those some other time.


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