According to the uses for which they are intended we must distinguish between -

I. Paving quarries, either plain or decorated with dips, without glaze. II. Facing quarries, plain or decorated, glazed. III. Stove quarries, plain or decorated, glazed.

Each kind requires special qualities, according to its destination; a facing quarry cannot be used for paving, and, even if certain stove quarries may under certain circumstances be applied to facings, the contrary, as we shall see, is certainly not true.

I. Paving Quarries

With respect to their ingredients, these quarries are divided into -

1. Quarries of ordinary clay decorated with coloured dips.

2. Stoneware quarries of various kinds.

I. Quarries Decorated With Dips

These must, without doubt, have been used, like enamelled bricks, by the earliest peoples, but their history is not known; we know well, however, that of the incrusted tiles which were made with such brilliant success during our Middle Ages. In the 8th century we find pavements adorned with designs roughly executed in relief, unglazed, but laid down with glazed quarries. According to Ame, the oldest quarry known dates from 853; it bears an inscription under the dark green and very thick glaze. From the 9th to the 11 th century, a period of ruin and struggle, scarcely any progress is to be noted in this branch of pottery. In the 11th century, monochrome unglazed pavements are found with incrusted designs; this simplicity was required in the Cisterian churches, and is in contrast with the rich decoration of the Clunician churches and abbeys. The death of Saint Bernard removed the severe rules which he had enacted, and it is actually to the Cisterian abbeys that we owe those important improvements in terra-cotta pavements at the end of the 12th century, due to the use of inlaid clays of various colours.

The pavements at the beginning of the 12th century are formed of small quarries of a single colour but of various shapes, often inlaid with a small piece of terra-cotta of another colour. The combination of all these bold-coloured squares, red, yellow, green, and black, form a kind of mosaic and give a fine effect, as may be seen by the pavements of that period still in existence at Saint-Denis (Seine), and Sainte-Colombe-lez-Sens (Yonne). The dominant colours of these pavements are black and green.

At the end of the 12th century inlaid squares appear, with or without glaze, in which black predominates. One of the most beautiful pavements of that period is that of Saint-Pierre-sur-Dives (Calvados). The 13th century made great use of these quarries in different colours; red predominates, yellow-green tends to disappear, black and brown are used to enclose divisions, but we observe in the manufacture less care and choice than in the 12th century; nevertheless some of these pavements are of great beauty.

In the 14th century the designs of incrusted quarries become more confused and more scanty; a profusion of initials, arms, and inscriptions are introduced into them; green and light blue appear among the colours; black becomes rare. Ornamented pavements of the 14th and 1 5 th centuries abound in Champagne and Burgundy.

In the 16th century we see, side by side with incrusted squares, faience quarries in which white, yellow, blue, and green predominate, and which form the marvellous pavements of Ecouen, Blois, Langres, etc. The bright colours of these quarries were soon preferred to the naturally duller tints of clay squares, and for more than a century, falfence pavements were in fashion. Then came the decadence, and in the 17th century, paving with incrusted quarries fell into complete oblivion.

It was the Englishman Wright of Staffordshire who revived the old processes, and it was Herbert Minton, assignee of Wright's patent, who succeeded in overcoming all difficulties and in manufacturing products superior to those of the Middle Ages in quality and decoration. The industry passed from England into France, where to-day there are important factories which make exclusively that type of quarry.

Manufacture

After the clays have been crushed, washed, decanted, and filtered, they are brought into a state fitting them for moulding by the following method.

The plaster relief of the pattern required is placed at the bottom of a plaster mould, and a first layer of clay of the first quality is applied with the hand to this relief, then another layer of less good clay, then another of inferior quality, and so on, until the proper thickness of the quarry is reached.

The whole is then placed under a quarry-press and strongly compressed, the relief at the bottom of the mould being printed in hollow on the clay; the slab is then removed from the mould and taken to the drying-room. When the paste is sufficiently hardened, the various naturally or artificially coloured dips are poured into the hollows in a state of paste, and the slab is left again to dry. After a sufficient desiccation, the surface of the quarry is freed from irregularities, it is polished, and drying is allowed to continue slowly, being completed in twelve to fifteen days. Firing may be effected in any suitable kiln.

One of the difficulties of this method of manufacture is the avoidance of the unequal contraction of the different layers of clay. The pastes used should therefore be prepared and tested with this view.

As the use of clays of different qualities is only intended to reduce the amount of fine clay, there is no reason why a quarry should not be made of the same clay throughout its thickness; moreover, instead of executing the design by means of dips applied to the surface, it may be made to traverse the whole mass of the quarry. The earliest pavements were formed in this way. The manufacture is more costly, but the products last longer. This question is now of secondary importance, for quarries of incrusted stoneware have entirely taken the place of those of ordinary clay.