Mosaic

I

Introduction

Mosaic, the art of creating figurative or geometric designs by embedding into cement small pieces of glass, stone, terracotta, or other suitable materials. Mosaic decoration is best suited to large plane surfaces; it is particularly effective on floors, interior and outside walls, vaults, and ceilings, but can also be applied to small panels and other portable objects. Mosaic was an art form especially well developed by the Romans and used extensively in Byzantine buildings and in Italian churches. Because the materials used in mosaics are relatively resistant to deterioration, many ancient mosaics have survived, and retain the same brilliance today that they had when they were originally laid.

II

Materials and Techniques

Mosaics in their classic form were made from small pebbles and later of cube-like pieces of marble, hard stone, glass, or terracotta, known as tesserae (Latin, dice).

To make tesserae, thin slabs of marble or of coloured stone were cut into strips, which were then cut or broken into cubes. Molten glass, which could be tinted in a range of colours by the addition of metal oxides, was poured out on to a flat surface to cool and harden. The resulting slab of coloured glass was scored with a sharp tool and broken into strips and cubes. Gold and silver cubes were made by applying gold or silver leaf to slabs of glass in pale shades. The surface was then covered with a frit (a thin layer of powdered glass) and heated in a furnace to seal the gold or silver between the layers of glass; the slab was then scored and broken into cubes.

Different styles of mosaic include opus tesselatum, simple geometric patterns; opus vermiculatum, small stones arranged in patterns of curved lines, or depicting people, animals, plants, or objects; opus musivum, mosaic on the wall in a house; and opus sectile, a pattern composed of larger stones of varied shapes.

Knowledge of ancient mosaic techniques is derived mostly from direct examination of specific examples; damaged mosaics in İstanbul provide explicit information. Walls to be covered with mosaics received a triple coat of plaster. The first layer (a mixture of lime, sand, and brick dust) was applied over the masonry to give a smooth surface. The intermediate layer (of lime, sand, and chopped straw), 1.25 to 5 cm (0.5 to 2 in) thick, was then applied, and was scratched or tooled to receive the third coat, called intonaco, of plaster of lime and marble dust, which was spread over a small area at a time; as much as could be completed in one day, for instance. It was then painted in detail in true fresco and immediately set with coloured tesserae to match the painted surface.

The tesserae were set into the painted intonaco one at a time, with resulting deliberate irregularities of the surface. These variations in surface planes catch the light and impart vitality to the finished wall. In many instances the tesserae are angled downwards in rows, with space between the rows; when viewed from a distance this gives the appearance of a continuous background.

III

Pre-Christian Mosaics

In Mesopotamia in the 4th to 3rd millennia bc, there developed a type of mosaic composed of slender cones of baked clay. The base ends of some of the cones were painted red, black, and white. The cones were embedded in mud brick walls to create a decorative and protective coating in geometric patterns, perhaps derived from textiles or matting. A large section of a Sumerian wall of half-columns (early 3rd millennium bc) from Erech (Uruk), decorated with these patterns, is preserved in the Staatliche Museen, West Berlin. See Mesopotamian Art and Architecture.

In Crete and on the Greek mainland in the Bronze Age (1600-1000 bc), water-worn pebbles were used to make floor mosaics. Pebble floor mosaics existed throughout the Hellenic Greek world from the 6th to the 4th century bc; notable examples have been discovered in Athens, Corinth, Delphi, Olympia, Olynthus, Pella, Assus, and Tarsus. The polychrome pebble mosaics at Pella in Macedonia, dating from about 300 bc, are excellent examples of the use of subtle variations in the colour of water-polished stones to create beautiful figural compositions, often depicting light figures against a dark background, delineated by either lead or ceramic strips.

Before the end of the 3rd century bc, pebbles were in large part replaced by tesserae cut from stone and sometimes from glass. The smooth surfaces of the tesserae made the mosaic more resistant to wear and tear and also made possible the creation of more detailed designs. Cutting the tesserae to small sizes and packing them closely together, craftsmen were able to create designs of impressive detail, realistically depicting scenes with human figures, animals, plants, and landscapes. See Greek Art and Architecture.

The Romans learnt the art of mosaic from the Greeks, and developed their own mosaic style. Mosaics then spread throughout the Roman Empire. Polychrome scenes of the late 2nd and early 1st centuries bc are among the earliest mosaics at Pompeii. The Alexander mosaic from the House of the Faun depicts the Battle of Issus and is thought to be a copy of a lost Hellenistic painting of the 4th century bc; the mosaic, however, was most probably executed in the 1st century bc. Mosaics from Antioch (modern Antakya in Turkey) dating from the late 2nd to the 6th century ad show a predilection for polychrome figural mosaics. Mythological themes, including the Judgement of Paris, Narcissus, and the Labours of Hercules, are depicted with great realism and in brilliant colours. See Roman Art and Architecture.

IV

Christian and Islamic Mosaics

In Early Christian mosaics of the 4th to the 6th century, decorative borders frame human figures, animals and birds, and frequently hunting scenes. In the Church of Santa Costanza in Rome, built about ad 350, the vaults carry mosaics of vine scrolls and geometric designs that enclose figures of pagan origin. See Early Christian Art and Architecture.