Porcelain Production

Technological outline of porcelain production

Contents of the porcelain paste:
-approximately 50% China-clay (kaolin), mixed with water, results a mixture with high plasticity, easily moulding,
-approximately 25% Feldspar that while fired turns liquid filling out the porous spaces, making the porcelaine body dense,
-and 25% Quartz that assures stability during firing, giving to the porcelaine body its transparency.

Three substances are combined with water in the drum mill and while mixed constantly are ground to below 63 microns. At the same time homogenized suspension is created. The resulting thin slip is transferred, from the drum mill into a tub through magnets, and screening it, then the porcelaine slip is pumping and filter pressing it.

As a result of filter pressing paste pies are produced. These paste pies pass through a vacuum press that removes air from the paste and homogenizes it. Depending on the opening of the vacuum press, the proper size, shape and diameter of the paste is cut for production. This is followed by several weeks of `rest'. The humidity of these ’body pies’ is approximately 22.5% - 26% at that time.

Further processing of these body pies can be done in two different ways:

On the one hand, slices cut from this body can be formed with the help of roller machines into plates and cups. This shape making process is done by rotating the roller heads and plaster moulds in the same direction, but at different speeds. After processing products are removed from the plaster moulds and are placed either in a dryer chamber or allowed to dry naturally on schelves. Handles are affixed to the cups by hand. After the drying and cleaning process products are ready for the next phase of production.

The body pies are placed in tubes and while constantly being mixed with water, supplements are added (soda, liquid glass) which assure good plasticity and casting proprieties at low water contents. (65% dry substances).
The casting slip is moved from a central system through gravitational hose and through faucets it is filled into the plaster moulds. This casting process is used for item such as soup tureens, large serving platters, coffee and tea pots, vases and figurines.

It takes approximately 15 minutes to achieve a wall thickness of 4-5 mm and the amount of water is absorbed by the porous plaster moulds. Once the appropriate wall thickness is reached, the remaining casting slip from the form is poured back into the central system and re-used. After a period of rest the newly formed products are placed on drying schelves .

If a particular item is made up of several pieces - as in the case of figurines — these are then assembIed together using the casting slip as an adhesive. After the drying and cleaning process the products are ready for the next phase of production.

Either worked by machine or casted, raw products are fired at 950 °C to ensure a solid texture that can be glazed. After this firing the product has an approximate porosity of 18-20%.

When it is submerged into the glaze for 3-4 second it absorbs water and at the same time a thin glaze is formed on the surface. The row materials of the glaze contains minerals very similar to the porcelain itself but with the firing they form a glassy fluid on the surface.

After glazing, the products are inspected and placed on the kiln cars. Then the products are fired either in chamber or in tunnel kilns at a temperature of 1360-1380 °C. After this process we can call it porcelain when the characteristic, dense texture of porcelain covered with a glass-like glazed surface leaves the kilns.

The qualified white porcelain is then hand painted and / or decorated with decals. The rnaterials used for the decorations are porcelain colors, kinds of metal oxides that have the characteristics of glass and have low melting points. The paints are applied to the surface of the porcelain by hand. In the case of a decal, they are applied using printing techniques to affix the design to paper. It is then soaked and applied to the surface of the porcelain and the backing paper is carefully removed. The porcelain paints do not contain any materials that would be hazardous to the health of humans.

As a finishing phase, after further inspections, the decoration is fired on to the porcelain at 820 °C assuring that the design will remain fixed to the glazed surface of the porcelain. The last step of the production process is the grading of the prepared product.