Tessera

For instance, a large body of surviving material from the Hellenistic period can be found in the mosaics of Delos, Greece, dating to the late 2nd century BC.

This produced a golden reflection emanating from in between the tesserae as well as their front, causing a far richer and more luminous effect than even plain gold leaf would create.

The glazed ceramic tiles have the color painted onto the top of the clay and then fired to a high temperature in a kiln.

It is opaque glass fired in large slabs in a kiln and then hand cut into small cubes with a hammer and hardy chisel.

[3][4] This tile is made with gold and silver leaf sandwiched between two layers of glass and fired twice in the kiln to embed in the metal.

Tesserae of a mosaic of doves drinking at a golden basin, 1st century AD, National Archaeological Museum , Naples , Italy
The unique illuminating effect of golden tesserae, Cappella Palatina in Palermo , Sicily , 12th century
A mosaic made from tesserae in St Peter's Basilica , Vatican State , Italy
A close up of the bottom left corner of the picture above. Close inspection of the full picture reveals the individual tesserae.
Apse mosaic of the Virgin Mother and Child, Hagia Sophia , featuring intensely luminous golden tesserae
Wooden block with hammer and hardy for cutting mosaic tiles.