Everything you always wanted to know about mosaics
The First Mosaics
The earliest mosaics were made in Greece in the 4th and 3rd centuries BC. These were made of black and white pebbles set into patterns - the use of colour was rare. By the 2nd century BC tesserae - small, specially hand-cut cubes of stone, marble, clay and glass - were being used. The use of tesserae meant that more complicated designs were possible.
How Were Mosaics Made?
The design was chosen, often from a pattern book of fairly standard designs, and the number of tesserae required was calculated and made in the right size, shape and colour. It has been estimated that the Rudston Charioteer Mosaic contains some 150,000 tesserae! Tesserae were either made in the stonemason's workshop or on the site where the new floor was to be laid. The mosaic had to be well-drained so if possible it was laid over a hypocaust system. Where there was no hypocaust a foundation of pounded sand, gravel or rubble was constructed. A layer of concrete, opus signinum (containing crush brick or tile) or lime mortar was then spread over the foundation. The tesserae were set into the top layer while it was still slightly wet and grouted with a slurry of fine mortar. The pattern was sometimes marked out on the surface first and the tesserae laid out using rules and set-squares. The mosaic was then rolled and polished.
What Materials Were Used?
Tesserae were made out of whatever materials were locally available. Materials were rarely imported into Britain specifically for mosaic-making. However, if chippings or broken fragments of imported marble, glass or pottery were available these were utilised. Different materials were carefully chosen for their colour. The Venus Mosaic, from the villa at Rudston includes tesserae in red, bluish black, grey, yellow ochre, brown, green and white.
How Did They Choose The Design?
The designs of mosaic floors were very similar throughout the Roman world, the same themes and motifs occurring again and again. This is partly due to the mobility of the craftsmen who moved around the provinces but also due to the use of pattern books from which home-owners would chose a suitable design. The pattern books do not seem to have been slavishly copied however, and some individuality was possible - for example, the use of the gladiatorial animals in the Venus Mosaic.
Who Made Mosaics?
Mosaic making was an alien art to the British before the Roman Conquest so many of the earlier mosaics would have been made by craftsmen from Italy or Greece. They probably trained local people in the art and it is likely that the Venus Mosaic was made by one of these native trainees.
How Do Archaeologists Lift Mosaics?
There are two principal methods of lifting mosaics. In both methods the mosaic is first secured by sticking gauze to its surface with water-soluble adhesive. The most common method is to lift the mosaic in sections. Vertical cuts are made along the design lines to minimise ugly joints when the sections are reassembled. As the bedding is carefully undercut boards are slid underneath and the section lifted.
The second method is rolling and this is the way most of the mosaics on display in the Hull and East Riding Museum were lifted. This is only possible if the bedding is fairly soft and the surface of the mosaic is level. The mosaic is slowly rolled up, usually in one piece, around a reinforced drum while being slowly undercut.