Porcelain Production |
| This page is not intended as a reference to producing ceramics, but more as a background to the ways different ceramics are produced, to help you to appreciate the difficulty in producing fine ceramics and why there are different styles. |
| The primary ingredient of ceramics is clay. Different clays produce varying qualities in the ceramics, and this enables historians to be able to precisely date a piece of ceramics, as well as differentiate between the people who made the ceramics. Modern ceramics will not be as easily deciphered, should historians look at them, because the process of making the ceramics has become standardized, with international companies building ceramics factories around the world, using the same process in each factory with the clays being brought from large quarries. Traditional ceramic makers did not benefit from the modern transport system, and therefore were restricted to using locally quarried clay. This led to the best ceramics manufacturers being centralized where the best clay was locally available. Cities like Jindezhen in China and Stoke-on-Trent in England became the foremost producers of fine porcelain, because there was a plentiful supply of the correct clays. These two cities were built around the ceramics industry and still function today as the primary manufacturers of fine porcelain. |
| Once the clay had been quarried the potter then took the clay and formed it into shape. Early pottery was made purely by hand and this can be seen were early pots are roughly formed and still show the finger marks of the potter. Eventually the potters wheel came to be used as it was found that pottery could be produced faster and more uniformly. Even today the potters wheel is in use, but where it was hand driven, now it is an electric motor that does the work. Now mass produced pottery is formed by machines without a human hand touching the clay. The mixing of clays from different places is common practice to produce a better potters clay. In Jindezhen it was found that they could produce fine porcelain consistently when they used a mixed clay. |
| Once the pot has been formed it then requires decorating or firing. Firstly we will look at the process of firing ceramics. |
| The process by which ceramics are formed is called vitrification and occurs at temperatures above 800° C. Different styles of ceramics are formed at different temperatures. Earthenware is produced within a temperature range of 800° C to 1100° C and forms a white, pink or grey coloured body. Stoneware is produced within a temperature range of 1200° C to 1280° C and forms a white or coloured body which does not have the density of porcelain. Porcelain is formed within a temperature range of 1200° C to 1400° C. Porcelain is white, glassy and very dense and if struck will ring with a high tone. |
| The control of Kiln temperature traditionally was hard and different parts of the kiln would have different temperatures. Traditional Chinese potters did not have the temperature measurement equipment available today and their Kiln was heated by wood, charcoal or coal. The Kiln relied upon the updraft created by the exhaust chimney to draw air over the fire and heat the inside of the Kiln. Vents built into the kiln and blocked with stoppers could be unblocked to allow air flow to slighty cool parts of the kiln, but this was the only method of control apart from the amount of combustibles being placed into the firebox. The Traditional style of Kiln produced many differing qualitiesof pieces as the temperature profile through the kiln could not be controlled as well as today's modern Kilns. |
| A Modern Kiln uses gas or electricity to heat air which is then blown through the kiln in large kilns. The temperature of the air can be precisely controlled before it even enters the kiln enabling mass production of ceramics with a known quality by producing a known temperature profile through the kiln. Modern kiln's for mass production will be open ended with the damp pots entering the kiln process on an automatic conveyor. The first process will be the preheating and drying of the pots and as the conveyor progresses further into the kiln the temperature is increased. Firing a pot takes a long time and the conveyor will keep the pot within the kiln for just the right amount of time to vitrify the clay. |
| The principle enemy of both the modern and traditional potter is air bubbles within the clay. Air expands when heated and will cause a pot to explode within the kiln as the pot is fired. Another problem occurs when there are differing thicknesses in the walls and base of the pot. The pot will vitrify at different rates if there are large differences in the thickness of the clay causing the pot to crack during the firing process. Rapid cooling of the ceramics after firing also causes problems with the pots, creating discolouring or breakage, however, cooling of the pot is sometimes used as a creative rather than destructive process. |
| Glazing of the pots can take place either before or after the first firing. If a pot is required to have a base colour withdecoration on top of it, the pot will be glazed prior to the first firing. It is also possible, especially in the case of porcelain, that the pot be fired with a decoration painted onto the base. Traditional glazes will have been applied by either dipping the piece into glaze, by hand painting the glaze, or by air blowing glaze onto the piece. It is normal on traditional pieces to find that a part of the pot remains unglazed, normally on the foot. This was done to prevent the piece from sticking to the kiln shelf or sagger (a protective casing of fire clay in which delicate ceramics are fired). |
| Application of a glaze as a base colour before decoration is called underglaze where as the application of a glaze over decoration is called overglaze. In the west, overglaze or onglaze also refers to lowfire, brightly coloured glazes that require a second or third firing. |
| There are many different methods of making and decorating ceramics. This is just the tip of the iceberg, but we hope it has provided some insight into the basics of ceramics production. |
