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CLAY BODY DEVELOPMENT
Our first clay body was Liguanea Clay from Kingston
which we had used in Art School. However, we soon became dissatisfied with the
porosity and tried to fire higher. Most pieces came from the kiln either
porous/leaking or overfired(warped or lean) and the heavy iron content darkened
any glaze put over it.. There is no local source of flux for earthenware glaze
and our stock of imported glaze materials were almost depleted. This was 1977
and importation (with its foreign exchange scarcity, import restrictions and
delays) was out of the question. We decided that what we really needed was a
stoneware body so that we could use the granite rocks from the Blue Mountain
area as a glaze flux. We spent a good deal of time riding around the country on
our motor cycle collecting sample of clay and promising looking rocks. A
series of experiments ensued using various combinations of Clonmel Clay,
Frazerwood Marl and Castleton Clay with granite rocks from the Wag Water River
bed roasted and crushed as a source of feldspar and mixed with a good quality
limestone from Brown's Town for glazes. As luck would have it The Todds,
American Potters who lived not far from us, decided to leave Jamaica and were
selling a ball mill which reduced the stress involved in pulverising the rocks.
These early experiments met with limited success but provided the base for later
developments.
Mixing a body based on Castleton Clay created some improvement (we could fire to cone 8 and use a local glaze)but introduced cracking problems. Any piece over a certain size and beyond a critical thickness would crack at the drop of a hat. Some pieces would survive the process but some would crack during drying while others would shatter after firing. Attempts to solve the problem - covering the pieces with cloth and plastic during drying, building a drying cupboard , introducing grog to the body- were unsuccessful. It appeared that the total shrinkage was not the cause of the cracking. Evidence suggested that the rate of shrinkage was at the root of the problem. To confirm this, shrinkage bars were made from the body and measured every hour over a twenty four hour period. The "drying hysterics" of Castleton Clay is the term coined by Donald to describe what he discovered as he tried to isolate the reason for the excessive cracking ie. the rate of drying was inconsistent resulting in sudden volumetric changes as the clay shrank. A body with Castleton Clay over a certain percentage also did not stand up well on the wheel. Many good pieces in which we had invested a lot of creative energy were lost during this period. We continued to use the Castleton body as it was inexpensive and a suitable alternative had not yet been identified.
In 1980 we had two exhibitions showing our improved stoneware body based on
Castleton mixed with some Fireclay which we had bought from the Todds. This body
stood up well at cone 9 and erratic cracking was reduced. It was not too
difficult to throw but was still rather dark and coarse for detailed scraffito
decoration.
The period of the eighties saw a switch from Hodges Clay to Frenchman Clay (both from the Black River area of St. Elizabeth). A gradual improvement in the quality of the body resulted with efforts being made to reduce the iron content and the particle size. In those days we hand picked the clay.As a result it was possible to get good quality Frenchman Clay.The first body based on Frenchman clay and Temple Hall granite was milled in 1987. An important factor in our body requirements was our desire to use celadon glazes. Early examples of Castleton Clay bodies show relief carving covered by white slip as a base for the celadon. The Hodges body still contained too much iron to show a good celadon. The smoother and whiter firing Frenchman Clay, however, provided a good base for the celadon allowing for more intricate detail. By the mid eighties we had to admit that throwing alone was not producing a
desirable number of pieces (and for wholesale and some sets) the desired
uniformity. We wanted to reduce costs and reach a wider market by offering a
more affordable product. |
Donald began research with the objective of developing the best body
from lighter firing refractory clays from St. Elizabeth which he was first
introduced to at the Scientific Research Council. A major breakthrough came when
Donald noticed a pile of pinkish sand on the side of the road in the Temple Hall
area. It turned out to be rich in Potash Feldspar with magnetic Iron and some
Mica as the main minerals of interest to a ceramist.The Iron could be extracted
and the Mica washed out leaving a light firing material suitable for fluxing
stoneware bodies and glazes. In 1982 we milled our first body based on Hodges
Clay from St. Elizabeth and the Temple Hall granite sand. The Iron taken from
the granite sand is milled and used as a glaze colourant and as brushed on
decoration.
We felt that we had a good product and it was time to
move to the next level, that of increasing volume of output. Donald began
research and experiments in developing a casting slip. With a successful casting
slip came the challenge of creating a mould line using our thrown forms as
models and the financial and logistical difficulty involved in developing and
managing a mould line without quality plaster and trained mould makers. The
introduction of slip casting (see picture to the left) coincided with the milling and bagging of Jamaican
clays, limestone, granite and silica sand by a local supplier. The small size of
the market, however, does not allow the supplier to put in costly quality
controls or carry large stocks. Unannounced variations in the composition of
bags of materials as well as sudden , unexpected depletion of stocks has forced
us to import some of the basic components of the body earlier this year 2000.