Earthenware
Earthenware is a porous ceramic fired at relatively low temperatures. Typically, it needs glazing to hold liquids.
Stoneware
Stoneware is fired at much higher temperatures, which allows the clay to become vitrified (glass-like), or nonporous. Stoneware is still usually glazed or slipped to increase its impermeability and for decoration.
Firing Temperature
Earthenware is kiln-fired twice, an initial "biscuit" firing at around 1,000 degrees Celsius and a second, glaze firing at around 1,100 degrees Celsius. Although the clay is less refined, stoneware is kiln-fired at 1,200 to 1,300 degrees Celsius to vitrify the clay.
Glaze
Refined earthenware is usually glazed bright white with hand-painted, transfer-printed, or decaled decoration. Stoneware has a variety of glazes (and clay slips) such as salt-glaze, alkali, lead, Bristol and Albany, but stoneware decoration is more limited to painting or stenciling.
Vessel Type
Refined earthenware is usually reserved for light-duty domestic objects such as serving dishes (plates, cups, saucers, etc.). Stoneware, with greater durability and impermeability, often is used for heavy-duty objects such as crocks, jugs and jars.