It is almost unnecessary to say, that the principal foundation of ceramic manufactures is clay, and that of the latter is chiefly composed the porcelain which in ordinary use, we recognise as the finest description of china ware.
This material is compounded of a clay derived from decomposed feldspar, calcined flints finely ground, and a proportion of powdered feldspar. These substances are kneaded into a dough by manual labour, in a mill or tub, into which a stream of water trickles.
When the mass is sufficiently uniform in colour and density, it becomes fit for the process of moulding, which is performed on a potter's wheel with guages, and other instruments. When nearly dry, the vessel which has been formed is transferred to another lathe or wheel, where its symmetry is perfected, and where it is burnished and smoothed with an instrument of polished steel.
After this, it is baked in a kiln, but as it still retains its porous properties, it has to undergo the process of glazing, which is effected by immersing it in a mixture, which on being exposed again to the action of intense heat, protects the porcelain surface with a vitreous covering.
It is not the material, but the additional labour, that constitutes the value of this manufacture; and as the more expensive kinds of porcelain are subjected to repeated firing in the kiln, an increased supply of fuel, as well as labour, is inevitable.