Ball clay is an extremely rare mineral found in very few places around the world.  The blue clays of the Bagshot beds found around Wareham are of the finest in the world. The main concentration of ball clay in Dorset is to the north of the Purbeck Hills centred around Norden. Its name dates back to the early methods of mining when specialized hand tools were used to extract the clay in rough cube shapes of about 30 cm. As the corners were knocked  through handling and storage these cubes became rounded and ‘ball’ shaped. Ball clays are sedimentary in origin.  Approximately 45 million years ago in tropical times an ancient river Solent washed Kaolinite (formed from decomposed granite) from its parent  rock on Dartmoor. (At this time the Isle of Wight was still joined to Purbeck.) As the streams flowed from upland areas the mixed with other clay minerals, sands, gravels and vegetation before settling in low-lying basins to form overlaying seams of ball clay.  Ball clays  usually contain three dominant minerals: from 20-80% Kaolinite, 10-25% mica, and 6-65% quartz.  In addition, there are other 'accessory' minerals and some carbonaceous material (derived from ancient plants) present.  The wide variation both in mineral composition and in the size of the clay particles results in different characteristics for individual clay seams within a deposit. 

Purbeck Ball clay has been used for thousands of years but large scale commercial extraction began in the middle of the 18th Century continuing to the present day with open cast workings at Povington, Arne and North of Wareham. 

Before the rise of Poole, Wareham was the port for the area, and 32,00 tons of cargo were recorded shipped from the quay in the 1860's. 

  

 

 

This view shows the old clay warehouse in Wareham from which ball clay was loaded on to ships. This building is now situated in the grounds of "The Priory" hotel.

 

 

 

 

The company now extracting in Purbeck is Imerys who bought out English China Clays in 1999. Imerys has kindly made a substantial donation to Purbeck Mining & Minerals Museum group of all their redundant buildings at Norden.

Extraction methods have constantly evolved. From an early date a specially shaped spade - or tubal - was developed, which was eventually superseded by the pneumatic spade. The clay has been quarried and mined. When mined the use of shaft mines and adits was common place in Purbeck as conditions dictated.

Initially the extracted clay was weathered, a manual process that required it to be spread across large "beds" in the open. In later years it was found that this process could be speeded up artificially by shredding.

Individual raw clay selections are blended carefully according to pre-determined recipes to provide a product with a consistent and predictable range of  characteristics and behaviour.  The first stage in processing then is to shred (or ‘kibble’) the blended clay into smaller, more regular lumps about the size of a golf ball.  Much blended clay is sold in this shredded form.  Further processing through drying and grinding yields powdered plastic clays and ceramics manufacturers (particularly in the sanitaryware sector) also have benefited from the development of refined ball clays which offer improved performance and reduced manufacturing process costs. Refined clays are available in ‘noodled’ and slurried form. Ball clays also are sold in a partially dried form, which consist of golf ball size materials that are not powdered. .

A vital material in ceramics - Ball clays are used in many different industries, but in particular form a vital component in ceramic manufacturing.  Kaolin (‘china clay’) produces a very white colour when it is fired, but used alone it is brittle and weak and must be mixed with ball clay to produce a workable, malleable raw material.  As a result of their sedimentary origin, raw ball clays have a wide range of colours. However, many of them are valued by the ceramics industry for their white-firing properties, which are determined by the levels of iron and other colouring/fluxing oxides within the clay.

 

Ball Clay Uses

Sanitaryware: A ‘ceramic body’ for sanitary ware typically includes 30% ball clay to provide plasticity and workability, 20% kaolin, 30% feldspar and 20% quartz/silica.

Tableware: Ceramic tableware utilizes ball clay to provide high plasticity and a good white-fired colour, combined with kaolin, feldspar and quartz.

Wall and floor tiles: Combined with talc, feldspar, quartz/silica and kaolin, ball clays are utilized for their plasticity and bonding properties.

Glazes and engobes: Ball clays are also used in the production of coatings for ceramic products to ensure the perfect finish.

Refractory clays: An ability to resist the effects of extremely high temperatures makes ball clay ideal for use in refractory products such as kiln insulation and kiln furniture.

Construction ceramics: Building materials such as bricks, clay pipes and roof tiles all contain ball clay.

Electrical porcelain insulators: You will find ball clays in the electrical porcelain components that provide insulation from high voltage currents.

Non-ceramic applications:  These include the construction industry; horticulture, agriculture, pharmaceutical and amenity industries; use as fillers and extenders in polymers, adhesives, plastics, sealants, medicines,  fertilizers and insecticides.

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