Making Ceramics Products:
How to obtain and process the clay
In the past almost every potter or ceramist used to get his own clay from the clay-pit after he found the right place. The field of clay is normally 0,5m underground but sometimes this depth can reach even 12m. The potter left the clay outside during the winter period where under the weather conditions the clay become to be highly plastic and usable.
In nowadays we have the special machines in the factories which help to speed up the whole process. All raw materials are weight, selected to enter another process. After few hours in the special mills where all material had been crashed properly all water has to be removed. When a dry clay body is heated, the first reaction is the loss of water by the clay particles.
Hand building techniques
Having covered how to hand-build pottery and ceramics using hand-building techniques, potter’s wheel and wheel-throwing methods. Nowadays we use mostly electric potter’s wheels to save our time. After the formation of products we have to leave them to dry when is needed to turn them time to time and control the drying process.
The bone dry pieces are then fired to bisque fire stage of about 850°C to 950 degree Celsius. The bisque pieces are then left to cool and removed from kiln, and a glaze is applied to them before firing for a second time to melt the glaze to glassy state at temperatures between 1060°C and 1310 degrees Celsius.
During processing it is grey green in colour and after firing it shows the typical Tuscan brick red. This clay is used to produce the traditional plates on a potter’s wheel, vases, jugs, cups and all other objects of a rounded shape. It can also be used to produce special shapes in plaster moulds like - for example – oval trays, which cannot be made on a wheel.
After the firing in the kiln we have a terracotta form. The next stage of the process is glazing. Each piece is dipped into liquid glaze, which we prepare ourselves, and when entirely coated in the glaze it is left to dry for a day or two.
A glaze is applied on pottery and ceramics for the following reasons:
1. To colour and decorate the ware for a higher aesthetic value
2. To strengthen the ware
3. To make the ware waterproof – unglazed earthenware will absorb water and bacteria can flourish in them
Glaze is a thin layer of glass or glass and crystals that adheres to the surface of the clay body.
It provides a smooth, non-absorbent surface that can be coloured and textured.
A glaze is that glass-like outer layer in pottery and ceramics that has melted to a glassy state in kiln fire but has not melted enough to runoff the wares to which it is applied on.
Metal oxides are mixed with glazes to give colours upon firing. The amount of oxide used, the temperature fired, the atmosphere of firing if reduction or oxidation, thickness of glaze, and presence of other metal oxides in the glaze all determine the final colours obtained. It’s all a question of trying, and to keep on testing for any good surprises in final results/colours. Keep good records of what you do and once you get a good colour that is interesting to you, confirm it again by following your log of records - and there you have your own glaze recipe to use for many more firings to come.
The paints are made from natural minerals and by mixing them in our own studio. Then the most time consuming part begins. Each piece is individually hand painted, allowing the personal style of each painter to appear.
The powder colour is mixed with water and then applied to the glazed surface of each piece. The most remarkable thing to notice at this stage is the flat, opaque nature of the colour before firing, and each painter must be aware of how these colours will change during firing to ensure that the correct tonality is achieved in the end. Second firing
The final stage of the production is the second firing. This transforms not only the colours, but also the glaze, which becomes a solid shiny surface that will survive well for many years. The gas fired kiln reaches a temperature of 940°-965° C (about 1700° F) in a twenty-four hour cycle, twelve hours to reach the maximum temperature and twelve hours to completely cool. Only then can we open the kiln and discover the results of so much patient work.