Clay is a product of the decomposition of rocks, particularly granite, also known as feldspathic rock, which is abundant all over the earth's surface. These rocks are decomposed through time from the many different physical actions such as erosion due to the wind and rain, earthquakes and volcanic eruptions. These activities eventually create the clay we use. Clay is highly malleable substance. It is this plasticity that enables clay to retain a given shape when molded and shaped by hand or by machine.
If the clay remains uncontaminated by iron or other metallic particles it creates a whitish clay referred to as Porcelain. Introduction of various metallic contaminants through erosion turn the clay grey or red.