176 Chapter 7
3.3 Firing Process
The firing process is the key step in the manufacturing process: the porosity
of the material is reduced and particles are connected by partial fusion and/or
sintering of amorphous constituents (Figures 12 and 13). Firing strengthens
the structure and determines the major characteristics of the ceramics, such as
the colour and the resistance against environmental attack.
The basic principle in turning a paste with high plasticity into a hard and
durable material is connected with dehydration: at room temperature most of
the absorbed water is already lost from the surface of the crystals. At a few
hundred degrees, the water trapped between the layers is removed and later,
structural OH groups are attacked. By thermal analysis it could be shown that
Figure 12Fragment of a Neolithic ceramic vessel (Romania, around 5000 BC), an overview
Figure 13Fragments of Neolithic ceramic vessel (Romania, around 5000 BC), a cross
section; SEM: the coarse structure with partial fusion of the grains is visible