Mosaics. Mosaic work (Lat. opus musivum) consists of small pieces of diversely coloured marble, glass, or other substances set together so as to produce a geometrical or artistic design. Mosaics are principally used for ornamental floors and pavements, and for the permanent artistic decoration of the walls of churches and other public buildings. The art is of ancient origin; by the book of Esther we may infer that it was practised in the days of Ahasuerus; but among the Romans it was very common, for scarcely have the remains of any ancient Roman villa been discovered without finding in it a mosaic pavement. These ancient pavements being composed of small tessere or dice of coloured marble, and rarely also of glass, are known as tessellated mosaics. The pieces used consist of irregular cubes varying from a quarter to half an inch in size, and they are carefully bedded in a cement surface set over a prepared concrete foundation. The designs, pictorial or otherwise, are produced by selecting and setting together, in proper position and relation, tessere of the required colour and size. The most famous tessellated mosaic of ancient Rome now existing is that obtained from Hadrian's villa at Tivoli, preserved in the Capitoline Museum at Rome, and known as 'Pliny's pigeons' from the subject it depicts. Under the Byzantine empire mosaic became a distinctively Christian art, employed for decorating the walls of churches with figures of the Saviour, apostles, saints, &c., and the remains of such Byzantine art form a link of great importance between classical and mediæval periods. The art was revived in Italy about the beginning of the 13th century, when it was employed with great effect for the decoration of churches; and since that time it has remained, with many fluctuations, a distinctively Italian pursuit. Modern mosaics are also made in Russia, forming a department of the imperial glass manufactory at St Petersburg; and in Paris some excellent work has been done. The cubes of opaque glass for mosaic pictures, technically called smalts (Ital. smalto), are of all possible varieties of colour, as many as 25,000 shades being prepared. With these the finest gradations in tone may be produced, and copies of any painting may be made, but mosaics of real artistic significance are simple in composition, and broad and sober in treatment. Italian mosaics are of two distinct classes—Florentine and Roman, the former being composed of pieces of stones or shells of natural colours shaped and inlaid in marble slabs according to the design to be produced; but it is limited in its application chiefly to floral scrolls and Arabesque designs. This variety of mosaic is extensively produced in India, having been there introduced by the Frenchman Austin de Bordeaux in the decoration of the famous Taj Mahal at Agra, whence it is distinguished as Agra work. Roman mosaic is made up of the small cubes above mentioned, and, while the larger wall decorations are composed of pieces which may be half an inch in size and upwards, small mosaics are composed of almost microscopical squares, these being used by jewellers for the ornamentation of brooches, small boxes, and miscellaneous bijous. Mosaic pavements are extensively made of small cubes or tessere of coloured marbles, and baked clay or terra-cotta similar to the ancient Roman tessellated pavements.
See Thomas Morgan, Romano-British Mosaic Pavements (1886); Parker's Church Decorations and Mosaic
Pictures (Archæol. of Rome, vol. xi. 1876); and Gerspach, La Mosaïque (1883).