Monday, July 09, 2007

Making Pottery

Potters start their work with lumps of moist clay and end it with finished pieces of pottery. The means by which such ends are accomplished vary widely and what follows should be regarded as an outline of one sequence of operations sometimes followed, chosen from the many that are practised.

Preparing the clay. A portion of clay is kneaded until it is thoroughly mixed and of even moisture content throughout. If at this stage the clay is too dry to use, water is added, and if the clay is too wet, it is allowed to dry out to the condition required. After mixing, the clay is wedged to remove entrapped air. When wedging clay by hand a ball of the material is thrown repeatedly onto a hard surface, to drive out the air. The progress of the operation may be checked periodically by cutting the clay with a wire and checking the cut surface for bubbles of air. Mixing and wedging are operations that can be carried out by hand, or mechanical mixers and wedging machines may be used. Machines used for wedging clay are called pug-mills.

Shaping the wares. Wares may be shaped by hand, by using the hands in conjunction with a machine such as a potter's wheel or by mechanical means alone. Other methods of shaping are also used, including slip-casting and pressing.

Drying and finishing. After shaping it is common for pottery wares to be air-dried to a leather-hard condition and finished by trimming off unwanted clay on a wheel, in an operation analogous to turning wood on a lathe, or perhaps by sandpapering the surface of the ware to a fine finish. Shaped but still unfired pottery is called greenware.

First or bisque firing. Greenwares are fragile and are sometimes given a first or bisque firing to harden them for convenient handling and to reduce the risk of breakage during glazing and decorating. In this condition the ware is called biscuit-ware or bisque-ware. Temperatures used for bisque-firing may be either higher than those used for final firing, or lower, depending on the characteristics of the materials used and the preferences of the potter.

Glazing and decorating. After bisque-firing the wares may be coated with a layer of glaze, often applied by dipping.

Second or glaze firing. The glazed wares are re-fired to melt the glaze and bond it to the clay body, thus forming a glassy covering on the surface of the pieces.

Enamelling. Glazed wares are sometimes decorated with coloured enamels and re-fired in a glaze kiln or muffle-furnace.

0 Comments:

Post a Comment

<< Home