Green clay from the same pit . . . . . . 12
Yellow clay (Picpus pit)....... 10
Arcueil clay (Fontainebleau pit)...... 6
Plastic Arcueil clay...... 8
Greenish clay-marl........ 36
While calcareous marl....... 28
Yellowish marly sand ........ 28
Green Fresnes clay...... 37.5
White marl ......... 30
Picpus fireclay ......... 20
Fontenay sand ......... 8
Gentilly clay ......... 2.5
The clays are prepared as usual by blending; each manufacturer has his own special processes according to the clays he has to treat. The quarries are moulded by hand in plaster moulds which have the pattern, if there is one, in hollow or relief on them. Presses may also be used.
The glaze for these quarries, which is always stanniferous and consequently opaque, has the white enamel as its base. The processes described in the general remarks on glazes may be used for their decoration, but the method most frequently employed is decoration on unfired enamel. In this way are made the thousands of common squares used for facing kitchen ranges, and, in France, principally manufactured at Ponchon (Oise) and Desvres (Pas-de-Calais).
The white enamel is spread over the quarry by immersion, and after drying the pattern is printed by means of a cut-out engraving or a stencil - plate over which a hard brush covered with the enamel paste is rapidly passed.
If the pattern includes beads, they are made by hand. This process, called "au pochoir," is carried out with extraordinary rapidity by highly-skilled workmen, and they succeed in producing quarries which can be sold finished, at seven francs a hundred or even less.
The decoration is monochrome, but it can be enriched with other colours either by the brush, or by the usual processes.
For outer facings, the quarries have a greater thickness; the unenamelled side, which is placed against the wall, bears hollows intended to increase the adhesiveness of the mortar.