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Clay is a type of fine-grained natural soil material containing clay minerals. Clays develop plasticity when wet, due to a molecular film of water surrounding the clay particles, but become hard, brittle and non–plastic upon drying or firing. Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impurities, such as a reddish or brownish colour from small amounts of iron oxide.

Clay is the oldest known ceramic material. Prehistoric humans discovered the useful properties of clay and used it for making pottery. Some of the earliest pottery shards have been dated to around 14,000 BC, and clay tablets were the first known writing medium. Clay is used in many modern industrial processes, such as paper making, cement production, and chemical filtering. Between one-half and two-thirds of the world's population still live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure.

Clay is a very common substance. Shale, formed largely from clay, is the most common sedimentary rock. Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. Mixtures of sand, silt and less than 40% clay are called loam. Soils high in swelling clays, which are clay minerals that readily expand in volume when they absorb water, are a major challenge in civil engineering.

Clay Media

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Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

From Egypt, Memphite Region, Lisht South, Pyramid complex of Senwosret I, north temple gateway, MMA excavations, 1913–14 Middle Kingdom

Archaic Greek Lekythos

Archaic Greek Lekythos

Attributed to the Capodimonte Group Archaic

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

From Egypt, Memphite Region, Lisht South, Pyramid complex of Senwosret I, north temple gateway, MMA excavations, 1913–14 Middle Kingdom

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

From Egypt, Memphite Region, Lisht South, Pyramid complex of Senwosret I, north temple gateway, MMA excavations, 1913–14 Middle Kingdom

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

From Egypt, Memphite Region, Lisht South, Pyramid complex of Senwosret I, north temple gateway, MMA excavations, 1913–14 Middle Kingdom

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

Sealing, Egypt, Middle Kingdom, 2040 – 1640 BC

From Egypt, Memphite Region, Lisht South, Pyramid complex of Senwosret I, north temple gateway, MMA excavations, 1913–14 Middle Kingdom

Archaic Greek Lekythos

Archaic Greek Lekythos

Warrior, horse, palm tree. Attributed to the Class of Athens 581 Archaic

Archaic Greek Kylix fragments

Archaic Greek Kylix fragments

Herakles fighting an Amazon. Attributed to the Segment Class Archaic

Roman Lamp
Terracotta conical cup

Terracotta conical cup

Rough clay, undecorated. Middle Minoan IIIA

Greek Terracotta oinochoe (jug)

Greek Terracotta oinochoe (jug)

The neck shows a man with two horses; a file of mules grazes in the panel on the shoulder; a bird perches on top of the handle. Geometric

Greek Terracotta tankard

Greek Terracotta tankard

On the neck, waterbirds. Geometric

Roman Terracotta lamp

Roman Terracotta lamp

Early Imperial

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