 Some potters like to achieve random effects by setting up the kiln so that ash created during firing falls onto the pots; this is called "natural" or "naturally occurring" ash glaze.Otherwise the ash is mixed with water, and often clay, and applied as a paste.Ash glazing began around 1500 BC, in China during the Shang Dynasty, initially by accident as ash from the burnt wood in the kiln landed on pots.