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Delve into the world of ceramics with this comprehensive guide to the science of clay. Learn about the chemical composition of clay, stages of dehydration, kiln firing, vitrification, history of pottery, techniques like burnishing and glazing, and more. Discover the ancient origins of pottery making, the evolution of potters' wheels, and essential techniques like slip, score, and coil. Uncover the fascinating art and craft of working with clay through this rich exploration.
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The Science of Clay: An Introduction to Ceramics Tara Maikranz
The Chemical Make-up of Clay • Al203 2Si02 2H20 • alumina, silica, water • Calcium carbonate, talc, grog, iron oxide • Plastic- malleable, easy to form and shape
Dehydration • Leather hard- beginning of dehydration process; stiff but moist • Bone Dry- green ware; next step in dehydration process; water has evaporated; unfired; hard but fragile
Kiln- enclosed heat source in which clay is fired (heated). • Dehydration process is essentially complete at about 500° C when the chemically combined water is driven out of the clay in the kiln.
Vitrification • Bisque; early stages of vitrification; clay is still porous; ready to glaze. • Vitreous- the pottery will no longer absorb water chemically and can never return to its original plastic state.
Bisque fire- bone dry clay fired at low temperature to bisque; early stages of vitrification; clay is still porous; ready to glaze.
History of Pottery • Pot making dates to about 10,000 BC in parts of Asia • Pinch or coil technique • Pit firing • Utilitarian • All of the earliest work was earthenware with no glaze
Burnishing • One of first surface techniques • Functional • Aided in the retention of water, but did not vitrify completely • Rub with smooth object at leather hard stage • Time consuming – usually takes at least three burnishings
Glaze • Silica • Forms a glass coating • Glaze fire- fire after glaze is applied to bisque ware. Glaze is non-porous after firing.
The earliest known glazes are found in the Nile valley about 5,000 bc • High temperature ceramics; stoneware, porcelain, glazes, were developed by the Chinese about 2000 years before the rest of the world
Potters Wheels are known to have been used in the Indus valley (Pakistan and northern India) about 4,000 BC but possibly earlier • True potters wheels appeared around 3000 BC in several areas of the middle east and China
Slip, Score, and Coil • Technique used to attach pieces of clay together • Scoring- scratching the surface of the clay • Slipping- adding water or liquid clay to scored surface • Put slipped and scored surfaces together • Coiling- add small coil (tube) of clay around slipped and scored edges and smooth to reinforce connection
References • http://www.depauw.edu/acad/art/Faculty/DHerroldWeb/pages/clay.html • http://www.mii.org/Minerals/photoclay.html • http://www.pottery.netfirms.com/assignments/assign/terms/glossary.htm#potparts