The properties of the clay ceramic products vary with the particle size distribution of the raw materials.

Whereas finely ground raw materials are required for fine ceramic products, mixtures of raw materials with different particle sizes are utilized for coarse ceramic products.

Coarse grinding of the raw materials with crushers, pan grinders, hammer mills or cross beater mills is often carried out by the raw material suppliers. Thus in ceramic manufacture only fine grinding is required, for which wet grinding in ball mills, in which greater communition effects are realized than in dry mills, is satisfactory.

The clay constituents of the ceramic pastes are produced during raw material processing in sufficient fineness < 40 µm so that they can be immediately made into a slip by adding water in stirring tubs. This is mixed with the suspension of feldspar and quartz from wet mills and filtered over a sieve to remove any coarse particles still present. Magnetic separators are used to remove iron-containing impurities which have entered the paste during milling and processing and which would otherwise introduce undesirable coloration into the ceramic product.

The preparation of pastes is determined by the intended forming process. Castable pastes with a water content of 30 to 35% are stabilized by adding flocculants. Clay-containing slips also contain 0.2 to 0.4% by weight of water glass and other sodium silicates or calcined sodium carbonate, as additives.
 
For the manufacture of turning pastes, the paste slip is dewatered with filter presses to water contents of 20 to 25% by weight, comminuted in a sieve kneader and formed in vacuum extruders into suitably sized slugs.

Complete drying of the paste is generally carried out by spray drying. The spray-dried granules produced can be utilized both in dry pressing processes and with added water for casting and turning pastes.

As a result of increasing energy costs, interest in dry processing technology, which avoids the expensive evaporation of water, has increased Mixing of the appropriate fine preground raw materials is carried out in intensive mixers (edge-runner mixers, Eirich mixers) and then just sufficient water is added to the homogenized mixture for the intended forming process. In these dry processes the removal of iron impurities is extremely difficult.

One aspect of the processing of clay-rich batches for quality products is so-called "draining" or "maturing" storage in damp atmospheres for several weeks or months (in China some of the clay for porcelain manufacture has been drained for several hundred years!) During storage, water probably seeps between the crystal platelets of the clay minerals with the aid of bacteria and a homogeneously moistened paste with improved plasticity is formed.