Ball clays are
kaolinitic sedimentary clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay part ...
s that commonly consist of 20–80%
kaolinite
Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral ...
, 10–25%
mica
Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
, 6–65%
quartz. Localized
seam
Seam may refer to:
Science and technology
* Seam (geology), a stratum of coal or mineral that is economically viable; a bed or a distinct layer of vein of rock in other layers of rock
* Seam (metallurgy), a metalworking process the joins the ends ...
s in the same deposit have variations in composition, including the quantity of the major
minerals, accessory minerals and
carbonaceous materials such as
lignite
Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...
.
They are fine-grained and plastic in nature, and, unlike most
earthenware
Earthenware is glazed or unglazed nonvitreous pottery that has normally been fired below . Basic earthenware, often called terracotta, absorbs liquids such as water. However, earthenware can be made impervious to liquids by coating it with a ce ...
clays, produce a fine quality white-coloured
pottery body when fired, which is the key to their popularity with potters.
Ball clays are relatively scarce deposits due to the combination of geological factors needed for their formation and preservation. They are
mined in parts of the Eastern United States and from three sites
[The Bovey Basin in South Devon, the Petrockstowe Basin in North Devon and the Wareham Basin in South Dorset.] in
Devon
Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon is ...
and
Dorset in South West
England
England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...
.
They are commonly used in the construction of many ceramic articles, where their primary role, apart from their white colour, is either to impart plasticity or to aid
rheological stability during the shaping processes.
History
The name "ball clay" is believed to derive from the time when the clay was mined by hand. It was cut into 15 to 17-kilogram cubes and during transport the corners of the cubes became rounded off leaving "balls".
The
ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelai ...
use of ball clays in
Britain
Britain most often refers to:
* The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands
* Great Britain, the largest island in the United King ...
dates back to at least the
Roman
Roman or Romans most often refers to:
*Rome, the capital city of Italy
*Ancient Rome, Roman civilization from 8th century BC to 5th century AD
* Roman people, the people of ancient Rome
*'' Epistle to the Romans'', shortened to ''Romans'', a lett ...
era. More recent trade began when a clay was needed to construct
tobacco pipes in the 16th and 17th century.
In 1771
Josiah Wedgwood
Josiah Wedgwood (12 July 1730 – 3 January 1795) was an English potter, entrepreneur and abolitionist. Founding the Wedgwood company in 1759, he developed improved pottery bodies by systematic experimentation, and was the leader in the indus ...
signed a contract for 1400 tons a year of ball clay with Thomas Hyde of
Purbeck,
[See Purbeck Ball Clay] enabling him to fire thinner-walled ceramics.
See also
*
Ball clay and the Stover Canal
*
Ball clay use in ceramic Coade stone sculpture
Notes
References
{{Pottery
Pottery
Geology of Devon
Clay
Industrial minerals