Stoneware quarries are used for paving sidewalks, yards, passages (Fig. 737), stables, factories, etc. They are generally 14 centimetres square and 4 centimetres thick; their colour is yellow, brown, or black. The surface of them is furrowed so as to prevent slipping and give a hold to horses' feet. The principal types (Figs. 729 to 736) are: the staircase quarry (Fig. 729), quarries striated in arabesques (Fig. 730), diagonally (Fig. 734), or in angles (Figs. 731, 732), the granulated quarry (Fig. 733), the "grand cross" quarry (Fig. 735).
Thus 739, 741, 742 are used for stables, yards, passages; 738 and 743 for side-walks; the plain square 738 is for factory hot-air chambers; and lastly, 744 is used as a kennel-stone.
According to their shapes, the quarries are cut in two medially or diagonally (Fig. 738) or diagonally only (Figs. 742, 743); the squares 741 can be divided into thirds or two-thirds, or into halves and quarters; and finally, the hexagonal quarry (Fig. 746) may be cut along AB or AC. Besides these, we have half-squares ready made (Fig. 740).
Figs. 729 to 737. Various Quarries from Pont-Sainte-Maxence (Defiance et Cie.).
Figs. 738 to 746. Ceramic Paving Squares (Muller et Cie.).
The Potteries district in Staffordshire is the principal and almost the sole centre in England of this manufacture. It was at Stoke-on-Trent, the chief town of the Potteries, that Minton began his attempts at the reproduction of mediaeval encaustic tiles. Since that time, now many years ago, the primitive processes have been perfected, and a certain number of large houses successfully produce quarries of this type.
Fig. 747. Direct-flame Kiln used in England.
In France, the manufacture of stoneware quarries inlaid with clays of different colours was introduced about the year 1855 by M. Boulenger the elder, of Auneuil, who remains still almost the only regular maker of that style of product.
Clays of special qualities are required for the manufacture of these quarries. The preliminary treatment consists of crushing in presence of water, and for that purpose the mills described on pp. 57 to 60 are used. Other mills, called block-mills (Fig. 748) are sometimes substitued; in these, the grindstones are replaced by large stones moved by the horizontal arms of a vertical shaft. The bottom of the pan is paved with hard stones, and a ring prevents the blocks from rubbing against the sides of it. The advantage of these mills is that renewal of the grindstones is avoided. Alsing cylinders (Fig. 789) may also be used. When the clay is properly tempered, it is sent to the filter press, or, more simply, is left in the open air until it attains the proper degree of desiccation. Plain quarries are made from the clay when reduced to powder by some method. This powder is placed beside the press, which is generally a screw-press worked by hand (Fig. 604). With one hand the workman fills the mould with the powder, which is moistened to the proper degree, and applies pressure with the other. This method of manufacture is a fairly quick one. After being removed from the mould the quarry is trimmed and polished, and then goes to the drying-room.
Fig. 748. Block-mill (Boulton).
But when incrusted quarries are to be made, the moulding is carried out by the ancient process which we have described in the case of ordinary clay quarries decorated with dips. This process requires a considerable amount of labour. The quarry is moulded with several layers of different pastes, the composition of which is such that their contraction is similar; the bottom layer lies upon a plaster mould, and by pressure the top of this mould is reproduced in hollow on the quarry. The latter is then taken from the mould and dried. When the paste is dry enough, the coloured dip, which is prepared separately in colour - mills (Figs. 701 to 704), is poured on to it, and it is again dried; then the second dip is laid on, the quarry is again dried, and so on. Finally, when all the dips have settled and are sufficiently hard, the excess is taken off and the pattern is disclosed; the quarry is then polished with a steel knife. This manufacture of polychrome incrusted quarries is less quick than that of the quarries of felspar base which we shall describe later.
After drying, the squares are fired in direct - flame kilns (Fig. 747), similar to those used for faience; they are the kilns most generally employed in England. At Stoke, for instance, their tops are seen in all directions above the roofs of the factories. These kilns are not very economical, but the price of coal is not high enough to force manufacturers to improve upon their system of kilns. Firing takes place at a temperature high enough to transform the clay into stoneware, thanks to its natural composition.
Concurrently with this process we now use moulding with dry clay, which is more rapid. It will be described later on under the head of Manufacture of quarries of felspar base.