What type of clay is described as porous and requires glazing to be functional?

The type of clay that is described as porous and requires glazing to be functional is earthenware. This clay body is known for its high porosity, which means it can absorb water and other liquids easily if left unglazed. Glazing is essential for earthenware items that will hold liquids or food, as the glaze will create a non-porous surface that prevents leakage and makes the piece more durable and hygienic.

Earthenware is often used for pottery, terracotta sculptures, and decorative items, but it cannot be used in its raw form for functional ware without the application of glaze. In contrast, other clay types, such as stoneware and raku, have different properties. Stoneware is fired at higher temperatures and is typically more vitrified and less porous, while raku is a specific firing technique that results in unique finishes but does not change the inherent properties of the clay itself to require glazing for functionality. Kaolin, on the other hand, is a fine, white clay primarily used in porcelain, which is not characterized by being porous like earthenware.