It is next dipped in liquid glaze and goes again to be fired, this time into the "glost" or glaze oven, which is lower in temperature. After coming from this second oven it is no longer "biscuit" in appearance, but is covered with a skin or coating of glass or glaze, which has amalgamated with the body underneath.
It is now ready for painting with enamel colours or for transfer-printing, which obviously is "over-glaze" decoration.
Lastly, after this decoration has been made, it goes to be fired for a third time, and is put into the enamel or "muffle" kiln, which is the lowest temperature of the three.
In effect, then, the "over-glaze" decoration is on top of everything, and obviously, when the piece is scratched in use, this decoration wears away first. This at once gives the reason for another process, known as under-glaze decoration, where the work receives the protection of the glaze.
As a postscript to this description of the three firings, it may be noted in passing that, in true porcelain, such as Chinese, Dresden, and Bristol (all hard pastes), the body and glaze are fired at one operation, the glaze receiving as high a temperature as the body.
CHINESE BLUE AND WHITE PORCELAIN PLATES.
Painted in dark blue under-glaze. Painted in light blue under-glaze.
The types from which English potters made their copies.
(In the collection of the Author.)
CHINESE BLUE AND WHITE PORCELAIN PLATES.
Painted in rich blue under-glaze. The "Willow pattern" and the "Aster pattern."
The types from which English potters made their copies.
(In the collection of the Author.)