|High-Quality Limited Edition Beer Steins|
The most common of the stoneware steins are om the Westerwald region. Stoneware is a product of clay heated so intensely, to about 1200°C (2200°F), causing the clay to be vitrified into stone. It is hard to scratch, even with steel, and is impervious to liquids. Thus, glazes have been added only for aesthetic reasons.
Furnaces capable of producing such heat took some time to evolve, but it is really the special clay required for stoneware that prevented earlier discovery of this product. Stoneware clay must be very plastic, free from metallic and alkali impurities, and fired with little (5% or less) shrinkage, no warping, and no cracking. Stoneware clays, sometimes called white gold, were originally mined out of potholes, the sides of which were supported by saplings. These clays are still being mined today, but extensive shaft and tunneling techniques are now used.