Ball Clay

The wide use of ball clay is mainly due to its contribution of workability, plasticity and strength to the bodies in drying.

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BALL CLAY is a variety of Kaolinite, like china-clay. It differs from china-clay in having high plasticity and less refractoriness. In chemical composition, ball and china clays do not differ greatly except that the former contains a larger proportion of silica. It has derived its name from the practice of removing it in the form of ball-like lumps from the clay pits in the UK. The main utility of ball clay is its plasticity and it is mixed with non-plastic or less plastic clays to make them ecquire the requisite plasticity. The high plasticity of ball clay is attributed to the fact that it is fine-grained and contains a small amount of montmorillonite. Over 85% of the particle sizes present in ball clay are of one micron or less in diameter. It is light to white in colour and on firing may range from white buff. Pyrometric cone equivalent to ball clay hardly ever exceeds 33.

Usually the following proportions (weight percent) of ball clay are commonly used invarious types of ceramics composition:

• Vitreous sanitary-ware 10 to 40
• Hotel china-ware 6 to 15
• Floor and wall tiles 12 to 35
• Spark plug porcelain 10 to 35
• Semi-vitreous white ware 20 to 45
• Saggar bodies 10 to 25
• Glass melting-pot bodies 15 to 20

The wide use of ball clay is mainly due to its contribution of workability, plasticity and strength to the bodies in drying. Ball clay, on the other hand, also imparts high-drying shrinkage which is accompanied by a tendency towards warping, cracking and sometimes even dunting. This undesirable property is balanced by the addition of grog.