Iranian Samanid bowl, 10th century. 
Glazed stoneware, diameter 11" (27.7 cm).

Early Muslim potters made use either of Soda and Potash 
glazes or of lead glazes. The former, an alkaline glaze, is very transparent, 
but it allows only a restricted range of colours. Iranian potters tended to use 
an alkaline glaze (and alkaline glazes tend to be used on frit ware, when this
was introduced in the 12th century). Egyptians and Syrians, by contrast, tended
to favour a lead glaze. This allows a wider range of colours, but those colours
tend to run.