This procedure continued virtually unchanged until the widespread adoption in the 1950's of the 'shredding' of clay into small pieces - a process first introduced in the1930's that originally used mobile turnip cutting machines (see photograph, left). Shredding makes handling much easier and, most importantly, enables the clay producers to blend together up to 20 or more different seams of clay, often from different production areas. This has helped them to compensate for the natural variation in individual seams and to produce blends that are consistent and meet their customers' specifications, especially for faster casting and faster firing.
Filling 50 kg-paper sacks with
clay that has been dried and pulverised to a fine powder,
The desire to produce controlled products for particular applications whilst optimising the use of marginal clays led in the 1970's to the development of ball clay refining using automated computer-controlled process equipment. Clays with too much lignite are made into a wet slurry and the excess lignite particles are removed by fine screens (sieves); clays with too much quartz sand are powdered and the excess silica removed by air separation. The resultant refined slurry and powder are mixed together into a paste, extruded in 'noodles' and dried for bulk handling. The product is also sold in a liquid or 'slurry' form.
The East Golds processing site at Newton Abbot in 2000 showing ball clay refining plants and product storage in the foreground, powdering plant at upper centre and a lignite processing plant for horticultural applications on the upper right.
For many years ball clay companies produced 'prepared bodies'. These are the various mixtures of minerals (such as ball and china clays, silica, feldspar etc.) that normally the potter prepares and then shapes, decorates and fires. WBB also produced 'calcined' clays - pelletised ball clays fired in a rotary kiln and then ground down and incorporated in a pottery body. Having already been fired, calcined clays reduce the expansion and contraction of the body when it is fired as a finished ceramic.
At the beginning of the 21st century, about 75% of ball clay production is sold in shredded and blended form, almost 10% in powdered form and over 15% is refined. Less than 1% is sold 'as dug'. Process control has become an essential skill of ball clay production.
The development of these progressive employment
practices created an environment in which the workforce was willing
to respond positively to the changes taking place and to develop their
skills through the training opportunities offered. As the physical
demands on the workforce diminished, the roles of maintenance fitters
and electricians became more important. Production increasingly required
the close collaboration of multi-skilled teams of geologists, drillers,
surveyors and quality control chemists working closely with process
engineers, ceramists and technical sales personnel to assess how best
to fulfil customers' needs with the complex sequence of clay seams
in the ground and use of the appropriate processing facilities.