Ceramics

WHAT IS CERAMICS?

Let’s start with the very definition of ceramics: Ceramics (noun and adjective) are those things made from materials, which are permanently changed when heated.

The key in ceramics is the change it undergoes in the firing process. For example, clay has chemically-bonded water in it which will cause it to slake down (disintegrate) when a dried clay object is put in water. Once heated (fired) to between 660⁰ and 1470⁰F (350⁰ and 800⁰C), the clay is converted to ceramic and will never dissolve again.

Watch the Prezi and learn all about ceramics and the stages of clay.

Greenware is the term given to clay objects when they have been shaped but have not yet been bisque fired, which converts them from clay to ceramic. It is the first stage in creating pottery, there are two stages under Green Ware that we will be talking about. Greenware is unfired pottery. It is very fragile. Greenware may be in any of the stages of drying: wet, damp, soft leather-hard, leather-hard, stiff leather-hard, dry, and bone dry. At this stage, it is still possible to work the object by adding more clay, or wetting it so it softens and then reshaping it. Greenware should not be used as-is before firing in the kiln.

LEATHER-HARD

The Leather Hard stage is where the clay is stiff and will hold its shape; join to other pieces; carve into; recycle. At this stage, the clay is still able to be set, carved, etc. It is no longer bendable or moldable. It is the step before it completely dries, which is called Bone-Dry. At this stage, the clay is still visibly damp (usually a darkish gray) but has dried enough to be able to be handled without deformation.

BONE DRY

Bone dry (adjective) is a term used to describe and identified greenware pottery that has dried as much as possible before it has gone through its first firing (the bisque firing). When held, bone-dry greenware feels to be at room temperature, not cool to the touch. Coolness indicates that evaporation is still taking place. Bone dry greenware is extremely brittle and will break apart very easily. Therefore, it should be handled as little as possible and great care must be taken when loading it into the kiln.

BISQUE

Bisque refers to ware that has been fired once and has no chemically bonded water left in the clay. Bisque is a true ceramic material, although the clay body has not yet reached maturity. This stage is also sometimes called a biscuit or bisque. It is considered to be the second stage in creating pottery.

GLAZE WARE

The Glaze Ware stage is the final stage in the making of ceramics. Ceramic glaze is an impervious layer or coating applied to bisque ware to color, decorate, or waterproof an item. In order for earthenware, like fired clay pottery, to hold liquid, it needs a glaze. Potters apply a layer of glaze to the bisque ware, leave it to dry, then load it in the kiln for its final step, glaze firing. The glazed item is carefully loaded into the kiln for the glaze firing. The kiln is heated slowly to the proper temperature to bring the clay and glazes to maturity and then slowly cooled again. Only after the kiln has cooled, can the kiln be opened and unloaded. This second kiln firing caused a remarkable change in the clay and glaze. Pots are transformed from a soft, fragile substance to one that is rock-hard and impervious to water and time.

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