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Production Process

The production process of Delft earthenware starts with the composition of the clay. It is made up of about 10 raw materials, of which kaolin, chalk, feldspar, and quartz are most essential. They are imported from England, Norway, the Czech Republic and France. Raw materials are carefully mixed with water into a liquid mass.

The liquid clay passes a set of magnets to remove any iron particles and is stored in large containers to be used for moulding.

Making Plates:

04-finishing-the-plate-k.jpgA smaller part of the clay is put in a filter press where most of its water is extracted. It comes out of the press as a pliable, plastic mass. This is then to make all kind of objects that have to be purely round, like plates and platters. First a clay ‘pancake’ is made on a rotating disk, a modern potters wheel. Then this pancake is laid on a plaster mould shaped like the front of a plate. The reverse side of the plate is formed by pushing a modelled knife in the rotating pancake. This knife is outlined like the backside of the plate and scratches the surplus of the clay off.
mould.jpg

Other Objects:

The liquid clay is used as casting slip for all objects that are not purely round and have ridges. The slip is poured into hollow plaster molds, which consist of 3 pieces: the front, back and top. The inside of the mold is ahaped like the object to be produced. The porous plaster sucks the water out of the clay, leaving a layer of drying clay on its inner side. After 20-30 minutes, when the object is dry and strong enough and has got the right thickness, the liquid surplus is poured out.

After some time, the clay is hard enough to be taken out of the mold without being deformed. Seams and irregularities are carefully removed and the object is put into the kiln to be fired for the first time, at a temperature of 1160 °C (2120 °F). After 24 hours the body, which is now called ‘bisquit’, is taken out of the kiln.

01-painter-k.jpgDecorating:

Delftware painters then paint the traditional decorations on the articles entirely by hand. Hair of martens and squirrels is used for the brushes. The paint is a black liquid, containing cobalt oxide dissolved in water. This enables the painters to create various shades of blue by adding more or less water. During the firing process the black cobalt oxide is chemically transformed into the typical blue color. For other colors other metal oxides are used.

Glazing:03-ovensleigh-k.jpg

Before this second firing process the decorated pieces are glazed. This is done either by dipping them into the glaze or by spraying. The glaze covers the decoration with an non transparent layer of white. During the second firing process at a temperature of 1200 °C (2192 °F), the glaze melts into a translucent layer of glass and the black paint turns blue. After careful quality control the object is ready to be used.