Tesserae
Roman word meaning cube (pl. tesserae)
Tesserae are the basic building blocks of mosaic and the term refers to a diverse variety of materials including marble, ceramic, glass and pebbles.

Interstices
The spaces between tesserae. These spaces are ultimately going to be filled with grout. The size of the interstices and the colour of the grout should be taken into account for the overall design.

Andamento
The generic word used to describe the general ‘flow’ of the mosaic.

Opus Regulatum
A Roman mosaic technique whereby regular square tesserae are applied in straight rows. The result is like a ‘brick wall’ pattern, often used to fill expanses of background.

Opus sectile
When a part of the mosaic, such as a head, consists of a single piece then this part is known as opus sectile.

Opus tessellatum
Roman mosaic technique using regular, square tesserae to make a rectilinear arrangement. Most frequently used to fill expanses of background.

Opus vermiculatum
Roman mosaic technique whereby tesserae are applied in a row around a main motif to create a halo effect and emphasize the setting lines of the design. If the opus vermiculatum is continued outwards to fill a larger area then this area becomes Opus musivum, the most rhythmic and lyrical of all the opuses (it literally means ‘pertaining to the muses.’)

Smalti
The Roman word for ‘melt.’ Smalti are small, chunky pieces of glass tesserae hand-made in Venice.

(Notes adapted from Mosaics – design sourcebook Martin Cheek)

Andrew Wynne 2000