It will perhaps be as well, before entering further into the consideration of the subject, to define and arrange the objects of our attention under general heads.
Pottery (Fayence, Terraglia), as distinct from porcelain, is formed of potter’s clay mixed with marl of argillaceous and calcareous nature, and sand, variously proportioned, and may be classed under two divisions: Soft (Fayence à pâte tendre), and Hard (Fayence à pâte dure), according to the nature of the composition or the degree of heat under which it has been fired in the kiln. What is known generally in England as earthenware is soft, while stone ware, queen’s ware, &c. are hard. The characteristics of the soft wares are a paste, or body, which may be scratched with a knife or file, and fusibility, generally, at the heat of a porcelain furnace.
These soft wares may be again divided into four subdivisions: unglazed, lustrous, glazed, and enamelled. Among the three first of these subdivisions may be arranged almost all the ancient pottery of Egypt, Greece, Etruria, and Rome; as also the larger portion of that in general use among all nations during mediæval and modern times. We shall be occupied with the glazed and enamelled wares: the first of which may be again divided into siliceous or glass glazed, and plumbeous or lead glazed.
In these subdivisions the foundation is in all cases the same. The mixed clay or “paste” or “body” (varied in composition according to the nature of the glaze to be superimposed) is formed by the hand, or on the wheel, or impressed into moulds; then slowly dried and baked in a furnace or stove, after which, on cooling, it is in a state to receive the glaze. This is prepared by fusing sand or other siliceous material with potash or soda to form a translucent glass, the composition, in the main, of the glaze upon siliceous wares. The addition of a varying but considerable quantity of the oxide of lead, by which it is rendered more easily fusible but still translucent, constitutes the glaze of plumbeous wares: and the further addition of the oxide of tin produces an enamel of an opaque white of great purity, which is the characteristic glazing of stanniferous or tin-glazed wares. In every case the vitreous substance is reduced to the finest powder by mechanical and other means, being milled with water to the consistency of cream; into this the dry and absorbent baked piece is dipped and withdrawn, leaving a coating of the material of the bath adhering to its surface. A second firing, when quite dry, fuses this coating into a glazed surface on the piece, rendering it lustrous and impermeable to liquids. The two former of these glazes may be variously coloured by the admixture of metallic oxides, as copper for green, iron for yellow, &c.; but they are nevertheless translucent, and show the natural colour of the baked clay beneath.
Vitreous or Glass-Glazed Wares.
The vitreous, silico-alcaline or glass-glazed wares, were of very ancient date and in all probability had their origin in the east, in Egypt, or India, or Phœnicia; indeed the discovery of glass, which has always been attributed to the latter country, would soon direct the potter’s attention to a mode of covering his porous vessel of baked earth with a coating of the new material; but the ordinary baked clay would not take or hold the glaze, which rose in bubbles and scaled off, refusing to adhere to the surface, and it became necessary to form the pieces of a mixed material, consisting of much siliceous sand, some aluminous earth, and probably a small portion of alcali, thus rendering it of a nature approximating to that of the glaze, and to which the latter firmly adhered. In some instances, on the finer examples which may probably have been exposed to a higher temperature in the oven, the glaze and the body of the piece have become so incorporated as to produce a semi-translucent substance, analogous to some artificial porcelains. In its nature this glaze is translucent, and accordingly we find that when ornamented with designs, they are executed directly on the “biscuit” or unglazed surface of the piece, which then receives its vitreous covering through which they are apparent. By means of an oxide of copper the exquisite turquoise blue of ancient Egypt, “scarcely rivalled after thirty centuries of human experience,” was produced. The green colour was, perhaps, given by means of another oxide of the same metal; violet by manganese or gold, yellow by silver or perhaps by iron, and the rarer red perhaps by the protoxide of copper. We also find that bricks and vases of similar glazing, brought to its greatest perfection in Egypt, were made by the Babylonians and Assyrians.
Throughout Babylonia the sites of ancient buildings afford fragments of glazed pottery. The glaze of those brought from Borsippa by the abbé Beauchamp, in 1790, was analysed and found to contain neither the oxides of lead nor tin, but to be an alcaline silicate with alumina, coloured by metallic oxides. A more recent analysis of Assyrian examples shows that with a base of silicate of soda or soda glass and oxide of tin the opaque white has been produced, being the earliest recorded example of “enamelled” ware. A small quantity of oxide of lead was also found in the blue glaze on tiles from Babylonia. At Warka, probably the ancient Ur of the Chaldees, Mr. Loftus discovered numerous coffins or sarcophagi, piled one upon another to the height of forty-five feet, of peculiar form, and made of terra-cotta glazed with a siliceous glaze of bluish-green colour. They are formed somewhat like a shoe, an opening being left at the upper and wider end for the insertion of the body, and closed by an oval lid which, as well as the upper part of the coffin, is ornamented with figures and plants in relief. They are supposed to be of the Sassanian period.
The metallic lustre in decoration was applied, apparently at an early time, to pottery glazed with a siliceous coating, and appears to have established itself in Persia. On specimens from Arabia it is also found, and its use in combination with this glaze may possibly have preceded the manufacture of lustred wares coated with the stanniferous enamel, by the eastern potters of the Balearic islands, Spain, and Sicily.
In northern India, at Sind, and in Persia, wares are made at the present day of precisely the same character as the ancient pottery under consideration. Pieces from the former locality, which were exhibited at the International Exhibition of 1871, are composed of a sandy argillaceous frit, ornamented with pattern in cobalt blue beneath a siliceous glaze. Indeed their agreement in technical character with some of the pottery of the ancient Egyptians and Assyrians, and with that produced in Syria and Persia during the fourteenth, fifteenth, and sixteenth centuries, is most remarkable. Persia also now produces inferior wares of the same class, specimens of which, as well as some of those from India, are preserved in the South Kensington museum: the engraving on the opposite page represents a wall tile (no. 623) of the seventeenth century.
We thus see how widely spread, and at how early a period, the use of this most ancient mode of glazing was established and brought to perfection. It was the parent of all those wares now known as Persian, Damascus, Rhodian, or Lindus.