Ceramics – A Closer Look
Did you know?
Clay used for ceramics is a naturally occurring material in the soil; it is composed of fine grained materials which are plastic when wet and hardens when air dried.
Clay types are broken down into primary and secondary deposits in the soil. Primary clays are known as kaolin and are located at the site of formation. Secondary deposits have been moved by erosion and water from their primary location.
Ceramics are made by taking mixtures of clay and water and shaping them into desired forms. Once the ceramic has been shaped, it is fired in a high temperature oven known as a kiln.
Depending on the mineral content in the soil of a certain place or region in the world the ceramic clay body and colours can range from dull grey to orange. Primary clays like kaolin are the basis for white body clays and porcelain. Bog clays are varied in colour the source to the 19 century ‘’yellow brick” making industry in Ireland. Textural clays and glazes are the preferred palate of the ceramic artist.
Types of Ceramics
Ceramics can be divided into categories based on firing temperature: low fire, mid-range and high fire.
Low firing ceramic also known as earthenware is a red and a white terracotta clay. Both the clay and the temperature allow for a bright colour palette.
High firing ceramics refer to both porcelain and stoneware ceramics, and it is known for its durability and strength, but the colour palette is limited. The clay fires to a near glass consistency and then the temperature suddenly drops and this vitrified substance becomes as hard as stone .
Stoneware is usually rough in texture and grey to brown in color. Porcelain clay is know for its white colour and translucent qualities.
How Ceramic are Made?
The most popular and familiar method for making pottery is called throwing. A mass of clay is centered on a powered spinning wheel. The clay in motion is formed with the hands.
Slab building is used in sculpture and pottery applications. Clay is rolled out into sheets, then shapes are cut from a paper pattern and stuck together with slip clay into a 3 dimensional form.
Coiling is used to make large pots; rolls of clay are formed and then stuck with slip, one on top of the other to make an urn shape.
Slip casting, involves liquefied clay called a slip. It is poured into a plaster mold. As the moisture is drawn into the plaster, a wall of hardened clay forms in the shape of the mold. When the wall reaches the desired thickness, the excess liquid is removed and the piece is allowed to dry and then taken out from the mould.
Glaze is the glass coating outside a ceramic piece. Although its purpose is to seal the vessel it is also the medium to which minerals and oxide colours extracted from the soil can be added to the glaze according to the makers desired finish to create various textures, effects and colours. The temperature range of the firing also creates varied and interesting ceramic finishes as seen in Raku. Also other interesting effects on the clay and glaze occur depending on whether the kiln firing is gas, electric, peat , wood and whether oxegen (oxidized firing) is present.
Ceramics are all around us – crockery, tile, bricks, toilets and art.
Ceramics are typically very strong and can be found in watch parts, car spark plugs, electrical conductors, phone lines, appliance coatings, space shuttle & aeroplane nose cones.
Ceramics are used by artists as their medium for their visual metaphor.
Some useful words
Kiln – A large oven or furnace used to fire/heat clay to a particular temperature.
Raku – Is a form of Japanese pottery that is often handmolded, the pieces made are often used as part of traditional tea ceremonies.
Slip casting – Is a technique where slip (liquid like clay) is poured into a plaster mould, the water is drawn out leaving a solid piece of clay in the mould.
Slab building – A technique where by rolled or flat pieces of clay are pressed together to build ceramic pieces.
Throwing – This is when a potter’s wheel is used to make ceramic pieces.
Coiling – A technique where clay is rolled out into a rope like shape which is then used to make pottery.
Earthenware – Is a type of ceramics it is heated at a relatively low temperature and is often used as decorative tableware.
Stoneware – Is a type of ceramics which is heated at a high temperature it is durable and often used in the home.
Porcelain – Is a type of pottery often informally called “china” it is white in appearance, it is often used for household items and decorative objects.
© Orla Kaminska 2011