Supermagnetism Improves English China
by Liz Clark
photo by Chris Mikami

One of the world's oldest industries - English clay mining -has been revolutionized by the use of high technology. Cornish china clay, the raw material used in a wide range of products from cups and plates, baths and basins, to paper and pills, is exported all round the world. One of the secrets to its high and consistent quality is a cryogenic superconducting magnet, thought to be one of the most powerful in the world.

The supermagnet is used by the Goonvean and Rostowrack China Clay Company, at St Austell in Cornwall, south western England where they process diamond clays for tableware, porcelain and bone china. The clays are processed through the machine, which operates at a field strength of 5 tesla, to reduce iron and thereby improve fired color. Editor's note: Anyone know what a tesla is? There will be a test.

Clays with a high degree ofwhiteness - for use in the paper industry, for example - and which may need further refining are also processed this way. Consistent quality is demanded by the various industries using china clays, and a fully equipped laboratory is used to evaluate the product at various stages of processing.

The company has four pits where china clay is mined hydraulically using high pressure water jets. A slurry containing quartz, K-felspar, mica, kaolinite and unaltered granite, falls to the bottom of the pit from where it is pumped over coarse screens into classifiers.

Residual sand and rock are not wasted, but are processed to make a wide range ofproducts suitable for the local construction market. Cornwall's reserves of clay are located within the St Austell granite mass that was formed 280 million years ago.

Interested in China clay?

The Goonvean and Rostowrack China Clay Company Ltd.
Goonvean Works, St Stephen, St Austell
Cornwall, England, United Kingdom, PL26 7QF
Tel: +44 726 822381
Fax: +44 726 822431

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