abaculus

Abaciscus redirects here. For the moth genus, see Abaciscus (moth).Tessella redirects here. For the moth genus, see Tessella (moth).1. A tessera (plural: tesserae, diminutive tessella) is an individual tile in a mosaic, usually formed in the shape of a cube. Also known as an abaciscus, abaculus, or, in Persian کاشي معرق.In antiquity, mosaics were formed from naturally colored pebbles, but by 200 BCE purpose-made tesserae were being used. Marble or limestone was cut into small cubes that were arranged into the design. Later, tesserae were made from colored glass, or clear glass backed with metal foils. The Byzantines used tesserae with gold leaf, in which case the glass pieces were flatter, with two glass pieces sandwiching the gold. This produced a golden reflection emanating from in between the tesserae, causing a richer and more luminous effect.
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(n.)
A small tile of glass, marble, or other substance, of various colors, used in making ornamental patterns in mosaic pavements.
  

N M
tessera/small cube of colored glass for ornamental pavements/wall mosaics

PIASTRELLA DI VETRO, MARMO O ALTRO MATERIALE USATA PER FORMARE PAVIMENTI CON DISEGNO A MOSAICO