These quarries have some of the qualities of stoneware, such as hardness, but their paste is not absolutely impervious, and even when entirely melted always remains slightly pervious. They are subdivided into -

1. Quarries Of Slag Base (Also Called Pont-Sainte-Maxence, Principal Place Of Their Manufacture)

They are made by mixing blast-furnace slag with special, and more or less refractory, rich clays. This substance, the residue of casting, is a double silicate of lime and alumina, with variable quantities of the oxides of iron and manganese; its great fusibility is due to the presence of lime. After having been crushed and reduced to powder, this slag is blended in a pug-mill with the clay; the mixture is then machine-expressed and cut to the required size. When the slabs thus formed have acquired a certain degree of consistency in the drying-rooms, they are stamped in the mechanical presses which have already been described, are again taken to the drying-sheds, and then fired in kilns.

The principal centres of this manufacture are: in France, in the l'Oise department, at Pont-Sainte-Maxence (Defrance et Cie.), at Auneuil (A. Boulenger), at Canteleu-Lille (De Smet et Cie.); in Belgium, at Jurbine and Tertre; in Alsace, at Sarre-guemines; in Germany, at Ehrang-lez-Trier, Saint-Johann, etc.

Particulars Of Stoneware Quarries Or Paving-Squares

2. Quarries Of Melting Clay

These are made in various factories which are easily able to procure what are called melting clays - namely, clays which, used alone, begin to fuse under a strong firing, and thus bring the molecules closer together. The quarries made of these clays are of the same shapes as those of Pont-Sainte-Maxence, and they are called artificial stoneware quarries, ceramic quarries, etc.