Soda Ash or Sodium Carbonate is a chemical with a number of uses. These include within the pottery industry as well as many other industries. Its primary use within the pottery industry is as a deflocculant, reducing the viscosity of the clay slip. This allows the clay to be more easily poured and manipulated without increasing the water content of the slip.
It can be used along with Sodium Silicate to help create a casting slip with the required properties for casting. Both of these chemicals allow the viscosity of the slip to be controlled. This ensures the slip can be poured as needed.
Soda Ash is also used for soda firing. This is a process where soda ash is added to the kiln to create effects on the finished piece.