The clay which is mined in Klingenberg’s underground mine since 1742 is a high quality and fire-resistant bond clay with a high homogeneity concerning its granularity (85-98% of its weight are corns which are smaller than 0.002 mm) its plasticity and purety and highly valuable pyrometrical qualities. The clay can be used for nearly all ceramical products, which don’t need to have a pure white colour.

The clay has a light to dark grey colour, sometimes also a black-grey to black colour which is caused by a higher content of humus. The raw material is very fatty and takes some time to get soggy in water. In order to blunge the clay it needs about 37% water. Its bonding qualities are extraordinary. The clay can absorb up to three or three and half time its own mass of materials which make it less fat. Accordingly to its high plasticity, the clay has got a quite enormous drying shrinkage, which is 10%. Without additives, which make the clay less fat, it is prone to tear and to twist. In fire the clay shows a very early sintering, which can be considered to be quite perfect at about 1100°C.

It also reacts well on liquefaction by alkalis.

The firing colour is yellow-white at low temperatures and yellow at high temperatures. Reduced firing causes a grey-violet to grey-brown tint.

The fire resistance was determined by SK33. The temperature of 360°C which lies between softening and sagging can be considered as very convenient.

The clay which is mined in Klingenberg (also pencil-clay) has got an established position in the pencil-industry because of the clay’s very good bonding qualities with graphite.

The chemical and physical qualities of the Klingenberg clay are only influenced by relatively minor fluctuations:

Average value of the rational analysis (1998-2001):