Secondary tone

Secondary clays (Latin secundus, the second) are types of clay that are mostly colored and much more plastic than kaolin . They were washed away from the place of their origin by watercourses or carried away by the sea or ice. During the transport, these clays absorbed all kinds of impurities and coloring oxides such as iron oxides and manganese dioxide . The longer the clays were in motion, the finer their crystal structures became , and the more sculptural they became until they were redeposited ( sedimentation on a secondary deposit). Secondary clays are also called sedimented clays . So clay deposits were formed, from which the clays are mined in clay pits today.

Secondary clays serve as stoneware clay, slate clay, refractory clay or earthenware (pottery clay).

Stoneware clays

This is often a mixture of fat and lean clays, sand, fireclay and colored clays. They are specially mixed for the intended use, must be plastic and have a wide range of processing. During the firing, stoneware forms a dense body and only absorbs 2% water.

Stoneware forms a good intermediate layer (buffer layer) with the glaze , this promotes higher mechanical strength.

Stoneware is used for turning, rarely as casting compounds, for the production of building ceramics , sintered goods , boil-proof and salt-glazed goods and many other purposes. Their firing temperature is 1,150-1,300 ° C.