Britannica Sources used in this answer

How did angled tesserae make Byzantine haloes appear luminous?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Bird mosaic — mosaic Mosaic floor fragment from a synagogue or church, cut stone with mortar from Israel, late 5th–6th century ce; in the Jewish Museum, New York City.

In Byzantine mosaic art, the luminous quality of haloes was achieved through the precise manipulation of light using gold and silver tesserae. Starting in the 6th century, craftsmen developed a technique of setting these reflective cubes at extremely sharp, irregular angles rather than laying them flat.1

By tilting the mirror-like ends of the gold and silver tesserae downward toward the onlooker, the artists were able to secure a maximum light effect, causing the halo to shimmer and appear as a radiant circle of light surrounding the heads of holy figures. This practice relied on the practical experience of the mosaicist, who would often adjust the angle of individual cubes to catch light from specific sources, such as nearby windows. In some instances, such as in the 9th-century mosaics of Hagia Sophia, silver cubes were also interspersed among the gold to further enhance the sparkle and brilliance of the divine light.12