Part II POTTERY AND PORCELAIN

Chapter 11. Porcelain  

PORCELAIN is subdivided into two kinds. The Oriental, true, or hard-paste porcelain was made first in the Far East and is composed of two natural ingredients—china-clay and china-stone— which form porcelain when they have been mixed together and heated to a temperature of 1,300 to 1,400 degrees Centigrade. The material formed in this way is extremely hard, white and translucent, and if chipped or broken shows a shiny and moist-looking fracture. So-called soft-paste or artificial porcelain is made from glass fused with clay or some other substance to make it opaque and produces a superficial imitation of true hard-paste; although difficult to manipulate, it does not need to be fired at such a high temperature. It differs in appearance from hard-paste in allowing colours to sink more into the glaze, and if broken or chipped shows a sugary granular fracture. A further type of soft-paste, bone china, was introduced in England in about 1800, and employs china-clay and china-stone combined with a white powder obtained from calcined bones. It is not as costly to make as hard-paste, is more manageable in manufacture and durable in use than soft-paste, and has remained to this day the most popular and esteemed English china.

AH types of clay wares are put into their finished shape before being fired in a kiln, and there are three principal methods of doing this.

Moulding or Pressing: by pressing a thin cake of clay into a mould; for instance, for making plates.

Casting: by pouring liquefied clay into a plaster mould, leaving it for a stated time and then pouring away the surplus. In due course the article is removed from the mould. The plaster absorbs moisture where it is in contact with the wet clay, as it dries shrinkage takes place and they separate easily. Figures are built up from many separately moulded pieces which are then assembled by sticking them together with wet clay. The man who does this is called a repairer, and he scrapes away all signs of his work before the piece is fired. On some occasions these repairers used marks; at Bow, Plymouth and Worcester a Frenchman named Thibault rendered his name phonetically as T° which is sometimes found impressed or in raised letters.

Throwing: this is a very old way of working, and employs a flat circular table which revolves by foot-treadle or other means. It is used for the making of vases and bowls; manipulation by the hands of the craftsman aided by centrifugal force forms the article.

One further method used in primitive times, and occasionally today by studio, potters, should be added: in this, vessels are built up with long ropes of clay coiled round and round. The coils are flattened on the surface, and it is claimed that this has the merit of producing wares without mechanical intervention that express more closely the mind and intention of the potter.

With hard-paste porcelain the ware can next be painted, glazed and then fired, but only a few colours (notably blue) will stand the great heat of the furnace. Most are applied after the glaze has been fired, and the piece is then re-fired at a lower temperature. Soft-paste porcelain is fired, glazed and re-fired, before it is painted and fired yet again. Underglaze colours can be used on soft-paste ware that has received its first firing, and is then in the state known as biscuit. At some factories particularly well-finished pieces were sold uncoloured and unglazed as biscuit-ware.

The marks of many factories were copied widely, and they are not a reliable guide for identification. The collector should aim at recognition by other signs, such as modelling and colouring and the type of paste, and treat marks as of secondary importance.