The ultimate and defining stage in the process of creating a ceramic
object is the firing. For most studio potters it is in the final glaze
(glost) firing that the clay body is melted to the required degree of
vitrification and the glaze is melted and fused to the surface of the
clay.
To some extent the magical changes that take place in a glaze firing
are a mystery to many. From a chemical point of view the processes are
so complex that they are not fully understood by scientists least of
all potters.
There are however some fundamental principles of firing an understanding
of which can help us to gain some control and therefore some consistency
in the quality of the fired work. Given that we have the correct mixture
of materials in a recipe and have applied the mixture in a manner consistent
with the requirements of a desired result, all that remains is to fire
in such a way that the melting process and the cooling process will produce
the kind of metamorphic change that we desire.
The factors that impact on the chemical processes that occur in firing
and cooling are:
- firing up temperature and time
- cooling rate
- the kiln's internal atmosphere that envelops the pots during the
heating and cooling process.
Variations in these factors will result in variations in the colour,
texture, fluidity etc of the glaze.
During this lesson we will discuss various methods of firing and look
at specific firing schedules or cycles and the impact that atmosphere
has on the chemical and physical changes that occur in the glaze during
the heating and cooling process. We will also talk about kiln structure
in terms of their ability to influence particularly the cooling cycle.