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; active and inactive ingredient in beauty products; and as a filler in paint, plaster, adhesives, and pharmaceuticals.
The English 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 known by the following other names:
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. The first discovery of fuller’s earth in the United States was near Quincy, Florida, in 1893; previously it was imported from England. In 1939 mines near Quincy produced half the U.S. production.
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.
Hills, cliffs, and slopes that contain fuller's earth can be unstable, since this material can be thixotropic when saturated by heavy rainfall.
Fulling is an important step in the production of woolen garments, and can be traced back to ancient times. Cuneiform texts from Mesopotamia mention a raw material, im-bab-bár (Akk. gaṣṣu ‘gypsum, plaster’), literally “white earth”, which was delivered to fullers for the finishing of cloth. There are several Biblical references to fulling (2 Kings 18:17; Isaiah 7:3 and 36:2; Malachi 3:2; Mark 9:3), but the materials used to whiten the fabric are not specified. Pliny the Elder mentions several types of fuller’s earth (creta fullonia in Latin) from a variety of locations, each with different properties and therefore different uses.
The first references to fulling mills are from Persia, and by the time of the Crusades in the late eleventh century, fulling mills were active throughout the medieval world.
Called 'Multani Mitti' ('mud from Multan') in modern day India and Pakistan, the use of Fuller's Earth across the Indian subcontinent dates back to at least 1879. While its household use and transportation by local carts in the Sindh region predates the 1800s, export by rail was first recorded in 1929 in British India.
In addition to its original use in the fulling of raw fibers, fuller's earth is now utilized in a number of industries. Most important applications make use of the minerals' natural absorbent properties in products sold as absorbents or filters.
The Sherlock Holmes story The Adventure of the Engineer's Thumb involves counterfeiters making fuller's earth bricks as a false explanation for their hydraulic press (which is actually being used to make counterfeit coins).