1. An Introduction to Ceramics
The Science of Clay:
An Introduction to Ceramics
Tara Maikranz

2. 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
The clay body is held together firmly, but not rigidly, by the collapsed molecules of alumina and silica which intermesh like a basket weave

3. 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 -

4. 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.

5. 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.
Vitrification- at the earliest stage, the molecules of silica and alumina begin to collapse together, partially filling the voids left by the escaped water and creating a relatively firm bond which gives the fired clay body its hardness and strength. Vitrification continues with the melting of some of the impurities in the clay, chiefly beginning with iron oxides. These combine and melt to form a glassy substance which flows around the remaining alumina molecules, gluing them together in a rigid bond.
At higher temperatures mullite, an alumina silicate characterized by long, needle-like crystals, begins to grow and becomes interwoven with the glassy substances in the clay body. Glassification and the growth of mullite combine to form an extremely rigid and hard crystalline structure in the clay body which gives stoneware and porcelain its characteristic clear ring when tapped.

6. Bisque fire- bone dry clay fired at low temperature to bisque; early stages of vitrification; clay is still porous; ready to glaze.

7. 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

8. 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

9. Glaze Silica Forms a glass coating
Glaze fire- fire after glaze is applied to bisque ware. Glaze is non-porous after firing.

10. 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

11. 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

12. 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

13. References