Is a bisque firing necessary, or can I skip straight to glaze firing?

Both the clay and glaze, particularly in the case of stoneware and porcelain, can be matured in the same firing quite successfully. However, gases produced in the clay from the burning of carbonaceous matter together with other gases from the dissociation of carbonates and steam from the chemical changes within the clay, all have to escape from the clay surface. It is much easier for this to occur without the hindrance of a glaze layer. When a glaze layer is present, the gases have to pass through this as well and can quite often leave the glaze with a mass of bubbles, or worse still become trapped in the clay causing it to inflate like a balloon. This latter problem is known as ‘bloating’. As you will see, these problems can cause an increased loss rate which more often than not negates any cost saving made from only having one kiln firing.