In this bowl, made in medieval Iran, lines are incised in the top layer of clay to create patterns and also to control the coloured glazes, whose lead composition caused them to run. This can be seen clearly in this example, where the green colour spreads outside of the incised lines. The rim and foot of this bowl probably originally come from seperate vessels. The design is typical of bowls made in Nishapur in the 10th century. A very similar bowl can be found in: Oliver Watson, Ceramics from Islamic Lands (New York: Thames & Hudson, 2004), 202, Cat. F.3.