The decorative vases in the Chamberlain & Co collections
are breathtakingly beautiful, but have you ever stopped to think about how they
are made?
Like all ceramics, they start life as clay: liquid clay, in fact, which is known as slip. These are shapes that are far too complex to be ‘thrown’ on the potter’s wheel, and so they must be cast in moulds. But shapes like these can’t just be cast in a single mould like half of an Easter egg; they must be assembled from a number of separately moulded pieces.
Every china company has its own unique recipe for slip, made
up of clay, water and a substance called a deflocculant to control its
viscosity. This liquid clay is poured into plaster moulds, which are left just
long enough for a thin layer of clay to form on the inner surfaces as the
porous plaster absorbs the water. It is a skilled task to choose the right
moment to pour out the excess slip for re-use, especially as the thickness of
the clay can vary considerably from one style of vase to another. For larger
vases the mould can be too large for this process to be done by hand, and
either a machine has to be used to tip the mould or a special design using a
removable plug in the base can be utilised.
After time has been allowed for the clay to dry and gain solidity, the mould is carefully opened and the delicate contents removed. Now that the clay is strong enough to be handled, the pieces can be carefully assembled, using a thicker form of casting slip to stick them together before they are left to dry prior to their first, ‘biscuit’ firing; for larger items the drying period may be several weeks. For more complex pieces there is a strict order in which the pieces must be assembled to ensure a uniform appearance.
The casting process extends beyond the sections used to assemble each piece, and also includes the props that will be placed in the kiln to prevent it from distorting or ‘slumping’ during firing at around 1235 degrees Celsius.
It is only when casting is complete that attention can turn to decorating the vase.
