First produced 5,000 years ago by the ancient Egyptians, who called it hsbd-iryt (‘artificial lapis lazuli’), the bright blue pigment was highly-prized in Antiquity, used to decorate tombs, sculptures, furnishings, and jewellery until the 4th century AD.
Traces of the colour have been found across the ancient Mediterranean, from decorations such as the ‘Pond in a Garden’ fresco in the tomb of the Egyptian scribe Nebamun, built in c.1350 BC, to a statue of the Greek goddess Iris, on the Parthenon in Greece.
The pigment was known to the Romans as caeruleum, and is mentioned by Vitruvius in his de Architectura, where he describes how it was made by grinding together sand, copper, and natron, and heating this mixture in a furnace.
Now, chemical analysis led by Tina Salguero of the University of Georgia, and recently published in the Journal of the American Chemical Society, has revealed that the pigment may have more than just aesthetic qualities.
The researchers found that the calcium copper silicate within Egyptian blue breaks apart into ‘nanosheets’ so fine that thousands would fit across a human hair.
‘The structure of the calcium copper tetrasilicate is naturally layered, and we found that these layers disassemble in hot water to provide nanometre-thick nanosheets,’ Tina told CWA.
These sheets emit invisible infrared radiation similar to the beams used by television remote controls, car door locks, and other telecommunication devices. The team hope that these discoveries could aid the development of a range of new technologies.
‘Calcium copper silicate provides a route to a new class of nanomaterials that are particularly interesting with respect to state of the art pursuits such as biomedical imaging, infra-red light-emitting devices (especially telecommunication platforms) and security ink,’ they write. ‘In this way we can re-imagine the applications of an ancient material through modern technochemical means.’