How is Pottery Made? – A Basic Guide
Raw unprocessed clay consists of clay particles and undecomposed feldspar, usually combined with quartz, mica, iron-oxides and other materials. However, apart from the coarsest earthenware, which can be produced from clay as found in the ground, most pottery is made from special clays mixed with other materials or ingredients to produce the desired results. The mixture is known as the clay body.
The unfired clay body (greenware) can be formed or shaped in many different ways: manually, using a potter”s wheel or other mechanical means (eg. jollying or jigging), or by using various types of molds, or ”formers” (consumed during firing) to hold the required shape. Once the body is shaped it is usually dried before firing, although some ceramic artists have developed “wet-fired” processes.
After drying, the clay body is fired (baked) in an oven called a kiln. Over the years, potters have resorted to various types of kiln, ranging from holes in the ground topped by a fire, to coal or wood fired ovens. Modern day potters typically used electric or gas-fired kilns.
Decorating the Clay Body
There are numerous ways of decorating the clay body. Some are used before firing, others afterwards. They include the following:
Patterns can be applied to the raw clay body, including reliefwork. Roman pottery features terra sigillata, a type of decoration not unlike the repoussé method used in metalwork.
Scratching, Sgraffito, Carving
Incisions or indentations can be made to the unfired body, often accompanied by the use of a slip (watery coating).
After firing, rather like a baker applies icing sugar to a cake, ceramicists use a slip, often combined with glazes, to achieve decorative effects.
After firing, some earthenware made from fine clays can be burnished or polished, as exemplified in the works by early Turkish and Inca ceramicists.
Like a varnish, a glaze is often applied to a fired item for decorative effect, although in many cases its primary function is to make the item impermeable. There are four main types of glaze: feldspathic, lead, tin and salt. Lead and tin are commonly used to glaze earthenware, while stoneware is usually salt-glazed.
One particular style of tin-glazed earthenware is known as maiolica. After its first firing, the clay body is dipped into a bath of fast drying liquid glaze and then hand-painted before being refired. The glaze interacts with the metal oxides of the paint to produce beautifully rich translucent colours. Originally invented by Islamic potters, tin-glazed maiolica reached its highpoint during the High Renaissance in Italy.
There are two basic painting methods used in ceramics: overglaze painting, a technique applied to a fired clay body already coated with a fired glaze; underglaze painting, which is used on a fired but unglazed body, including those coated with as-yet-unfired glazes.
An advanced decorative technique utilizes metallic mixtures of (eg) powdered gold, silver, copper or platinum to achieve a range of colours and effects. When applied to a fired body, gold produces a purplish hue, silver a straw colour, copper anything from lemon yellow to gold or brown, and platinum a silver tone.
This decorative method includes the use of transfer printing, as well as modern lithographic methods.