Fuller's earth

Fuller's earth is any clay material that has the capability to decolorize oil or other liquids without chemical treatment. Fuller's earth typically consists of palygorskite (attapulgite) or bentonite.

Modern uses of fuller's earth include absorbents for oil, grease, and animal waste (cat litter) and as a carrier for pesticides and fertilizers. Minor uses include filtering, clarifying, and decolorizing; and as filler in paint, plaster, adhesives, and pharmaceuticals.

The name reflects the historic use of the material for cleaning or "fulling" wool by textile workers called "fullers". In past centuries, fullers kneaded fuller's earth and water into woollen cloth to absorb lanolin, oils, and other greasy impurities as part of the cloth finishing process.

Fuller's earth is also sometimes called "bleaching clay", probably because fulling whitened the cloth.

Fuller's earth consists primarily of hydrous aluminum silicates (clay minerals) of varying composition. Common components are montmorillonite, kaolinite and attapulgite. Small amounts of other minerals may be present in fuller's earth deposits, including calcite, dolomite, and quartz. In some localities fuller's earth refers to calcium bentonite, which is altered volcanic ash composed mostly of montmorillonite.

In 2005, the United States was the largest producer of fuller's earth with an almost 70% world share followed at a distance by Japan and Mexico. In the United States fuller's earth is typically derived from deposits of volcanic ash of Cretaceous age and younger (glacial clays do not form fuller's earth). Fuller's earth deposits have been mined in 24 states.

In the United Kingdom, fuller's earth occurs mainly in England. It has been mined in the Lower Greensand Group and the Vale of White Horse, Oxfordshire. The Combe Hay Mine was a fuller's earth mine operating to the south of Bath, Somerset until 1979. Other sites south of Bath included Frome, Lonsdale, Englishcombe, Tucking Mill and Duncorn Hill. Although these sites had been used since Roman times, William Smith developed new methods for the identification of deposits of fuller's earth to the south of Bath. Other English sources include a mine near Redhill, Surrey (worked until 2000), and Woburn, Bedfordshire, where production ceased in 2004.

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