Modern earthenware may be fired to temperatures below 1200 degrees celsius, the usual practice in factories and some studio potteries. Thus absorbing of water up to 8%. Earthenware has lower mechanical strength then porcelain or stoneware.
Starting with stoneware and porcelain clays, firing them to high temperatures up to 1222 degrees celsius, which vitrifies the clay. This renders the water absorption 1 to 2 percent, classifying it as water resistant, thus making it winter hardy (glazed areas are impervious).
Raku is a type of firing of low firing process that was inspired by traditional Japanese Raku firing. It dates back to the early 1550s especially for the Zen Buddhist Masters. Raku firing really is one of the most natural techniques that you can encounter in pottery. So while the pieces look incredible, they are not really used for functional pieces. But they can be used for indoor bonsai. A lovely fact about Raku is that is name literally translate as "happiness in the accident".