Clay Making & History of Pottery

Here at the pottery we use large amounts of clay, as a matter of fact each of the "Durand Water Filter Systems" requires 15 to 16 kilograms of wet clay to form the 4 components, that when fired weigh in at about 10 kilograms.

We require certain qualities of our raw material, the clay needs to be workable when thrown on the "potters wheel". The clay must be of a constant quality to enable many pieces to be "fired" together in our large furnace.

To find the best results possible from our pottery we needed to learn a little bit more about this most amazing of materials, clay, and we also found out a little about the history of pottery.

The History Of Pottery

Pottery : Vessels and objects, which are made of clay and hardened by subjecting it to high temperatures

Historically, pottery making is one of the most widespread and oldest of the arts. Pottery is simple because it is the most elemental and difficult because it is the most abstract. 

When did the art of pottery first begin? Most reference books claim it started between 9,000 - 10,000 years ago in the area now known as the Middle East. Recent findings claim to carbon date American Indian pottery back as far as 25,000- 30,000 years ago, long before recorded history began. Pottery probably started around the Paleolithic or Old Stone Age and is amongst the oldest of artifacts that have been uncovered. Unlike metal, wood or cloth, pottery is resistant to corrosion or disintegration. 

Fired clay is the only material on earth that does not change with time. 

Throughout the ages cultures around the world have used clay for many purposes. Some of the earliest pieces found were animal and female figurines probably used for rituals and ceremonies. Pottery was mainly for utilitarian purposes like storing grain or dried materials. The earliest pieces were shaped by hand from crude clay dug from the earth, and left to dry in the wind and sun to harden. This form of pottery was not useful for storing water, as the shape would eventually collapse when the liquid was absorbed into the clay. A clay lining smeared inside a basket of woven reeds was discovered to work better to carry liquids. 

Heating of the clay pieces was the next evolvement in clay objects. Possibly this was discovered when heating a clay lined basket of food. Another theory is an accidental falling of a clay vessel into the fire. However it occurred the discovery that fire could make clay objects more permanent was when the art of ceramics was born.

Chemical changes occur in clay when it reaches 900°F or 500°C. The clay utensils after being heated or fired would keep their form when used to carry water or liquids. This first form of "firing" pottery was achieved by digging a hole, placing the clay object in it, then covering with wood.

Clay was also used to scribe the beginning of written words. Uncovered in Mesopotamia dating back to 3,000 B.C., tablets made of clay contained the first form of language. 

Today the nature and type of pottery is determined by the composition of the clay, the way it is prepared, the temperature it is fired at, and the type of glaze used. Pottery comprises of three distinctive types of ware. Earthenware, Stoneware and Porcelain. 

Pottery fired at "lower temperatures" is known as Earthenware, it still remains slightly porous and liquids will eventually come through the clay body. Earthenware was the first form of pottery. Clay bodies used can be either reddish in colour (like terracotta), tan or brown, or a gray to black colour. Different coloured slips were made by adding water to clay and mixing it together. This could be applied for decoration.

Today using glazing techniques, earthenware can be made to hold liquids.

The next evolvement in ceramics was the discovery that by subjecting the clay piece to an even higher temperature the clay body became non porous. Clay will vitrify at about 2,900°F or 1,600°C. Clay bodies used for stoneware can be red, brown, gray, white or black. This type of pottery, known as Stoneware was used as early as 1400 BC in China, then Korea (57BC-935AD) and Japan during the 13th century. 

When tea was first imported to Europe from China in the early 17th century, each chest had a red stoneware pot with it. These pots were quickly copied throughout Europe in Germany, Netherlands and England. Today stoneware is used mainly by artist potters.

Porcelain was first made in China around 618-907AD. This clay body was made from Kaolin (a white china clay) and petuntse ( a feldspathic rock). The petuntse was ground to powder and mixed with the clay and fired to 2,650°F or 1,450°C. The petuntse would vitrify while the clay held the shape. Porcelain is smoother and finer clay and is usually white (with a slight blue or gray tinge) or translucent when fired. 

While experimenting with porcelain clay bodies in England during the 18th century, Josiah Spode II added bone ash (made by roasting and grinding cattle bones). This resulting clay body is known as bone china and has become the standard in English porcelain today.

Historical Methods of Shaping Clay

Plasticity in clay allows it to be shaped in many different ways. In the beginning clay objects were formed by hand. 

Hand shaped methods:-

  • Pinch Pot- A ball of clay can be pinched into a desired shape.

     

    Pinch Pot

     

  • Coil Pot- Clay can be rolled between the hands to form long coils. The coils can be placed in rings built up layer by layer to form the shape. You can smooth or scrape the clay on the inside of the walls to finish it.

     

    Coil Pot

     

  • Slab Method- By rolling or flattening clay into slabs you can create square, rectangle, or cylinder shaped objects.

     

    Slab Method

Moulding was another of the earliest methods of shaping vessels or objects of clay. Indigenous people smeared clay into the lining of woven baskets and then placed them into the fire. The basket or "mold" would burn off and leave the desired shape with the impression of the mold on the exterior. The Greeks advanced this method by pressing clay into already fired pieces to obtain the desired form.
In 1945 plaster of paris molds were developed in Staffordshire, England. By utilizing slip, which is clay mixed with water to create a liquid or pourable form. When slip is poured into a mould the plaster absorbs the water leaving the clay shape in the mold.

Potters Wheel- When the potters wheel was invented the potter could add rhythm and uprising movement to their concepts of form. 
Comprised of a flat disc that revolves horizontally on a pivot. The disc acts as the worktable and the potter would push it around by hand. 

Pictures of stone and wood pottery wheels have been found on Egyptian tombs dating back to 3000 BC. The handwheel was set in motion by a stick that fits a notch in the wheel, this type was classically used in Japan.
With the addition of a flywheel separate from the wheel head and mounted in the frame, the kick wheel was developed in 16th century Europe. Operated by the potter using their foot to spin the flywheel. A foot treadle was added in the 19th century, and in the 20th century electric wheels with variable speed motors for more control came into use.

To throw a pot on a wheel head requires a vast amount of manual dexterity. Bernard Leach (a famous English potter) says " A potter is one of the few people left who uses his natural faculties of heart, head and hand in balance- the whole man".

The potter first puts a lump of kneaded clay onto the wheel head. As the wheel spins rapidly they use two hands to manipulate the clay until it is "centered". 
When the cylinder of clay is in the exact center the potter will then insert a thumb into the top of the cylinder and presses down. He or she then continues to expand the shape by pulling up the sides of the piece with two hands one on the inside and the other on the outside.

The walls are kept thick so they can then be shaped into the desired form. While it is still rotating the potter then forms the lip again using one hand on either side.
Here is a short video of one of our potters, "throwing" one of our water filter containers.

Jollying or jiggering was developed in the 18th century and is a mechanical adaption of wheel throwing. This method is used to produce mass amounts of one shape. Simular to a potters wheel, it has a large head which contains a mold of the desired shape, such as a plate, cup or bowl. The interior of the object is shaped by pressing the clay against the head while the exterior is shaped by a metal profile, which moves against the clay. 

Drying & Turning

To fire pottery without breaking the clay it must be air-dried first. When the clay is leather hard you can turn or finish the greenware (unfired pottery) piece. Some pieces return to a wheel head for trimming and finishing. Handles are added at this stage if required. Stamping, or carving a design might be added at this stage if desired.

Glazing & Decorating

Even the earliest pottery was usually adorned in some way. The artist left impressions with their fingers or carvings with a stick.

Pottery can be decorated before or after firing. When the clay is about half dry or leather hard bits of clay can be pressed into the pot. 

Impressing, incising, stamping, carving, piercing and sgraffito- finger marks pressed into the clay or impressions from a rope, basketry or straw, drawing on the pot with a stick or carving away the clay were how some of the earliest pieces were decorated. Sgraffito or "scratched" is when a different colour slip is applied to the clay piece and then the slip is scratched through leaving the artists design in the contrasting colour. Another contrast can be achieved by applying another colour to the scratched area.

Slip decoration- by using ochres and earth pigments a watered down mixture is applied to the clay to add a different colour. A design can be etched into the slip to allow the contrasting clay body to show through. 

Underglaze and Overglaze Decoration Painting- Applying a painted design to pottery was also an early development. Pottery can be painted on before or after firing. Primitive man used different coloured pigments and ochres to decorate their ware. Today there are a variety of products available to use to decorate before a pot is glazed leaving a contrasting design in the finished piece. 

Burmished or Polished Ware- After an earthenware piece made of fine clay is fired you can burmish or polish the outside to finish it. Burmished ware has been found in Turkey dating back to 6500 BC. Most Incan pottery is red polished ware.

Glazing- Earthenware (fired at lower temperature) pottery will hold water, but is still slightly porous. This means the water will permeate through the clay walls eventually and leak. In a hot dry climate this can be used as an advantage to cool the contents of the vessel by evaporation, especially if left in a breeze or wind.

Porousity does have disadvantages the main being it will leak fluids, and can not be used for storing milk or wine. Therefore the art of glazing followed quickly. On stoneware and porcelain, which is fired to the point of vitrification, glazing is for ornamental purposes. 

Glazing of pottery dates back to 5000 BC. The fired piece was covered with a ground glass powder in a water base and then fired again. The fine glaze particles fuse and become a glass like layer over the clay body. Glaze is a form of glass and consists of minerals such as silica or boron, mixed with a stiffener, such as clay and fluxes and a melting agent, such as lead or soda. 
Today there is a wide range of glazes and glaze recipes available.

Firing

After the piece is finished and thoroughly dried the pottery is fired. The first pieces of pottery were fired by using a hot wood fire. Later coal, gas and electricity were used to power kilns or ovens. Different effects are achieved by the type of kiln used, the type of fuel used, how the kiln is stacked, composition of clay bodies, oxidizing the flames, and reducing the oxygen inside the kiln. 

We use a gas fired fibre kiln. It consists of 22 burners and is an "up draft" design which allows us to keep a consistent temperature in all areas of the kiln. 

Bibliography

  • A History of American Indian Pottery by Susan Peterson ©1997 Abbeville Press and the National Museum of Women in the Arts
  • The New Encyclopedia Britannica, Volume 17, Macropedia Knowledge in Depth ©1990 By Encyclopedia Britannica Inc
  • Encyclopedia Encarta 2005 version
  • A History of Pottery- Warren E Cox ©1972
  • Ceramic History for Potters www.ceramicstudies.com
  • Ceramic Art Comment and Review An Anthology of Writings on Modern Ceramic Art ©1978 by Garth Clark 

     


     

    "Making of Clay"

    Clay is formed by water, heat and pressure eroding away rocks. It is a natural product of the earth. The geological process of mountains and ridges being pushed up and formed and then being worn down again by weather creates clay. Clay can be found in the earth, soft and ready to be formed. Or it can be made up from the different raw, dry materials mixed with water. It can be modeled, pounded, flattened, rolled, pinched, coiled, pressed, thrown on a potters wheel,cast into molds, scored, stamped, extruded, cut or spun. These natural materials are not only used in pottery but also in the making of glass, brick, tile insulators and elements used in electronic devices, cements, plaster and lime. Clay is one of the only materials which doesn't have much value on it's own but can be made into valuable product.

    "A Visit To The Clay Factory"

    These images like all others on this site are copyrighted,
    but may be used free of charge for educational purposes.

    Jon and Judy hop on a plane to visit Walkers Ceramics in Victoria, where their clay is made.

    David Walker met us on arrival. We arrived to find a busy workshop full of activity.

    Edgar Walker started manufacturing clay in Mitcham Victoria in 1885, along with his sons and grandson, Geoffrey Walker. They ran a large tile producing plant and also supplied technical colleges with clay, glazes and ceramic materials. In 1955 Geoffrey and Constance Walker established "Walker Ceramics". Now David Walker has taken over from his parents, continuing the family tradition in clay that is still going strong 4 generations later. Ceramics is one of the first useful arts to be developed by man and it continues to be an essential part of our society. Walkers supplies hobby and commercial potteries as well as schools with clay, glazes, oxides and tools.

    Let's start at the beginning of the process. Here are the large bays of raw materials, such as silica, alumina, feldspar, bentonite, etc. used to make the various clays. By adding different raw materials and in different ratios they are able to produce specifically designed clays for different uses. Some are designed for "throwing on a wheel", some for hand building, sculpting etc.

    The raw materials are added together and then crushed and sifted.

    The dry product is mixed with water and then filtered through screens to remove any unwanted objects.

    The wet clay is pumped into large tanks to be mixed .

    After the clay is thoroughly mixed it is pumped from the large blue tanks into the filter presses seen on the right of the picture.

    This is the pump which delivers the clay to the press. It also removes any unwanted metals by utilising a large magnet.

    The filter press is a series of large canvas bags which are filled with the wet mix. The large metal ends tighten down to remove the excess water from the clay.

    Here is David showing us how the filter press works. Next the large slabs of clay are removed from the press.

    Slabs of clay sitting on pallets waiting to go through the pug.

    Jon is looking at the large pugmill which de-airs and mixes the clay into an even consistent texture. Then extrudes the clay into continuous blocks and bagged.

    David is bagging the finished product. (Rare photograph - not seen for years - David bagging a product !!!!!)

    Here are the finished bags. After stacking them on a pallet they are loaded onto a truck to bring to our workshop in Beechmont.

    Each of these blocks of clay weighs in at 10 kilos, so we use about one and a half blocks for what is our most popular product the 12 litre water filter systems.