Firing
Firing is the central stage of the pottery making process.
It is most fascinating, but also the greatest cause of frustration for the studio potter.
It is almost impossible to control fully. There are different ways to fire pots,
the most common are in an electric kiln (pottery oven), a gas kiln or a wood firing kiln.
Pottery can be fired once, or various times depending on the desired result.
Commonly, pots are biscuit fired first and once again after the glazing.
Firing can be done in oxidising or reducing atmosphere.
This refers to the air surrounding the pots in the kiln chamber.
Normally there is an oxidising atmosphere, but smoke provoked by the firing itself
or by combustible material, reduces the oxygen causing various effects on the glazes.
Iron glazes change from brown to green ('celadon'), and copper glazes
turn bright red (sang de boeuf) instead of green.
Salt glazes are obtained by throwing common salt (soda) in the firing chamber;
this combines with the silica and alumina present in the clay,
creating a 'glaze' on the surface of the pots.
Primitive types of pottery were fired in open pits, filled with combustible material,
but could never reach high temperatures. In the Far East, kilns were built on the side of hills;
the fire was set at the bottom and the heat passed through.
Early stoneware was fired in kilns where the flames were first directed towards the top, then at the bottom and so on, so reaching  higher temperatures.
The Chinese separated the ware from the fire, by building chambers
fuelled through openings on the floor;
this cleaner firing atmosphere enabled the making of more refined ware like early porcelain...