This paste is the base of the Deck faiences, whose brilliancy and decorative effects are comparable to the finest ancient Persian faiences, and which are now freely manufactured, thanks to the generosity of the inventors in publishing their processes. The paste is prepared by crushing in a dry state a frit composed of: 85 parts of Fontainebleau sand, 7 parts of carbonate of potassium, 3 parts of carbonate of soda, and 5 parts of chalk. To 1 5 parts of this frit are added 25 parts of refractory white clay and 60 parts of flint. The addition of 6 to 8 parts of chalk gives a harder clay, more easily cut but more liable to lose shape in firing. The paste is white, not very plastic, and is difficult of treatment, which is hot an obstacle since it is intended for small smooth surfaces; its total contraction may be as much as 2 per cent.
The quarries are moulded by hand or in the press; after drying they are fired, and if necessary finished on the grindstone. Although they are white, they are dipped to give more delicacy to the colours and to render the biscuit less absorbent, thus permitting of greater uniformity of colouring. The manufacture is more troublesome, but the results are much superior.
The dip is composed of 75 parts of frit, 15 parts of chalk, arid 10 parts of white clay, to give it a little pliability; the whole is crushed fine and diluted with water to the required consistency. The dip is applied by dipping or sprinkling, and is fixed by firing; it is then decorated with finely ground colours diluted in the muller with a little gum arabic. These are applied with the brush, each tint in turn, avoiding impastes, which the glaze would not be able to dissolve and which would give a dull appearance. The piece is then covered with a glaze, crushed not too fine in a dry state, and containing -
Carbonate of potassium...
Carbonate of sodium...
The temperature of firing is about 1000° to 2000° C.