850 design may be of various degrees of elaboration, from the simplest, almost monochromatic, geometrical pattern to the most elaborate picture, with figure-subjects represented in colours of countless gradations. The earliest existing specimens of mosaic belong to one of the less important branches of the art namely, the ornamentation on a small scale of jewellery, ivory thrones, and other furniture, or more rarely of some elaborate archi tectural ornament. Most of this earliest sort of mosaic resembles in execution what are called cloisonnee enamels. In the Louvre and in the British Museum are preserved some very beautiful ivory carvings in low relief, some from Nineveh and others from Egypt, in which figures of deities, ornaments formed of the lotus and papyrus plants, and royal cartouches are enriched by small pieces of glass or lapis-lazuli and other gem-like stones, which are let into holes made in the ivory. Each minute piece is separated from the next by a thin wall or cloison of ivory, about as thick as cardboard, which thus forms a white outline, and sets off the brilliance of the coloured stones. The favourite pattern in this sort of work for decorating the larger sur faces appears to have been suggested by the feathers on a bird s wing. See IVORY, vol. xiii. pi. vii. fig. 3. Recent excavations at Tel al-Yahudfya in Lower Egypt have brought to light some mosaics on a larger scale, but treated in the same way. These are caps of columns, wall tiles, and other objects, either of white limestone or earthen ware, in which designs, chiefly some forms of the papyrus, are formed by brilliantly-coloured bits of glass or enamelled earthenware, let into a sinking in the tile or column. This form of mosaic was employed by the Greeks : the Erechtheum at Athens, built in the middle of the 5th century B.C., had the bases of some of its white marble columns ornamented with a plait -like design, in which pieces of coloured glass were inserted to emphasize the main lines of the pattern. Another, quite different sort of mosaic was known to the Egyptians of the Ptolemaic and Roman periods. This is made entirely of glass, and is extremely minute. The finest known specimen is in the British Museum : it is a small tablet about three-eighths of an inch square, apparently the bezel of a ring, on which is represented the sacred hawk, every feather on the bird s wing being produced with a great number of colours and tints, each quite dis tinct, and so minute that a strong magnifying glass is required to distinguish its details. The way in which this wonderful little mosaic was pro duced is extremely ingenious. Numbers of long sticks of various-coloured glass were arranged in such a way that their ends produced the figure of the hawk ; other sticks of blue glass were placed all round so as to form the ground. The whole bundle of sticks of glass when looked at endwise now presented the figure of the hawk with a blue background, immensely larger than it afterwards be came. The bundle was then heated till the sticks melted together, and the whole thick rod, softened by fire, was then drawn out to a greatly-diminished thickness. In this process the relative positions of the sticks of coloured glass forming the design were not altered. A slice of the rod was then cut off, and its faces polished, the design, much reduced in size, of course being equally visible at both sides of the slice ; and thus the microscopic minute ness of the mosaic was produced, with astonishing delicacy and refinement ; many slices, each showing the same mosaic, could be cut from the same rod. The more important use of mosaic has been on a large scale either for pavements or for walls and vaulted ceil ings. Mosaic for these purposes has by many writers, both ancient and modern, been divided on various systems into classes; perhaps the simplest classification is thefollowing: I. For Pavements : (a) Tesselated , in which the design is formed of small cubes, generally of marble, more rarely of glass or clay ; (6) Sectile, formed of larger pieces of marble, shaped and cut so as to fit accurately one with another. II. For Walls and Vaults: Fictile or vermicu- latcd ; pieces of opaque glass, in small cubes, arranged so> as to form complicated pictures. This classification is not altogether satisfactory, more than one method often being employed in the same mosaic ;. as, e.g., in the " opus Alexandrinum " of medieval writers., which is often partly tesselated and partly sectile. Until Roman times we know but little of these kinds of mosaic. There is some evidence (in Pliny and other writers) to show that elaborate mosaic pavements, At$o- CTT/KUTOV or Xi$oXoy->yji.a, were made by the Greeks in the 4th century B.C., or even earlier ; but most of the nu merous fine specimens of tesselated work still existing in Greece, such as those at Sparta and Athens, must be re ferred to the time of the Roman occupation. The best examples of Hellenic mosaic are some pavements dis covered during the recent excavations at Olympia (see fig. 1 and Ausgralmngen zu Olympia, 1877-82). Among the Romans the use of mosaic, both of marble and opaque glass, was very extensive. According to Pliny (H.N., xxxvi. 25), they derived this art from the Greeks, but not until the time of the Third Punic War, 146. B.C., while glass mosaics for Avails, " vitreae parietes, " were a recent invention in his time. Many of these have been found at Pompeii ; most commonly they are used to decorate niches for fountains or statuettes. Judging from the description given by Yitruvius (vii. 1), and an examina tion of numerous specimens of Roman tesselated mosaics, FIG. 1. Greek Pavement from the Temple of Zeus at Olympia. the process of manufacture was the following. The earth- was first carefully rammed down to a firm and even surface ;: on this was laid a thick bed of stones, dry rubbish, and lime, called "rudus," from 6 to 9 inches deep, and above this another layer, 4 to 6 inches thick, called "nucleus," of one part of lime to three of pounded brick, mixed with water ;: on this, while still soft, the pattern could be sketched out with a wooden or metal point, and the tesserae or small bits of marble stuck into it, with their smoothest side upper most. Lime, pounded white marble, and water were then mixed to the consistency of cream, forming a very hard- setting cement, called " marmoratum." This cement, while fluid, was poured over the marble surface, and well brushed
into all the interstices between the tesserae. When the