materialsclay

Clay, in the context of materials science and crafts, is a natural earthy material composed primarily of fine-grained clay minerals that form layered silicates containing water. When wet, these minerals are highly plastic, allowing them to be shaped by hand or with tools; as they dry they stiffen, and when fired they convert to ceramic materials.

Most common industrial clays fall into kaolinite, illite, and montmorillonite groups. They are classified as primary clays (formed in the original rock) or secondary clays (formed by weathering and redeposition). Fired clays become ceramics; firing temperature and flux content determine the product: earthenware (low-fire, approximately 900–1150 C), stoneware (high-fire, approximately 1200–1300 C), porcelain (very high-fire, approximately 1300–1400 C).

Processing involves mining, crushing, aging and grinding to achieve uniform particle size, followed by wedging or mixing to adjust plasticity. Forming methods include hand building, wheel throwing, and extruding. After shaping, the pieces are dried, sometimes bisque-fired, glazed, and then fired to mature the ceramic body. Clay-based products range from pottery and sculpture to bricks, tiles, and cementitious additives in some concretes.

Key properties include plasticity when wet, drying shrinkage, and porosity in the fired state; vitrification varies with composition and firing, affecting strength and water absorption. Safety considerations include inhalation of fine dust containing silica. Environmental aspects involve mining impacts and energy use for firing; various clays can be combined with fluxes and feldspars to tailor melting behavior and properties.