An Introduction to Ceramics The Science of Clay:.

An Introduction to An Introduction to CeramicsCeramics

The Science of Clay:

The Chemical Make-up of The Chemical Make-up of ClayClay

DehydrationDehydration• 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.

VitrificationVitrification• 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 PotteryHistory 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

BurnishingBurnishing• 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

GlazeGlaze

• 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 CoilSlip, 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

ReferencesReferences

• 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