Egyptian blue
The first color people made from scratch, over 5,000 years ago. Under infrared light it still glows.
- Made from
- Sand, lime, copper and alkali, fired
- Chemistry
- Calcium copper silicate (CaCuSi4O10)
- Party trick
- Glows in near-infrared
Egyptian blue is the oldest known synthetic pigment: not dug up but cooked. Heat sand, lime, a copper source (ore or bronze scrap) and a little alkali to around 850–950 °C, and you get blue crystals of calcium copper silicate. The earliest known example, on a bowl from Hierakonpolis now in Boston's Museum of Fine Arts, dates to around 3250 BCE.
Egyptians painted tombs, statues and coffins with it for three thousand years, and the Romans called it caeruleum, probably from caelum, the sky, a root shared by our word cerulean. The architect Vitruvius gave a recipe in the 1st century BCE, and Roman sources say a man named Vestorius brought production from Alexandria to Pozzuoli near Naples. After Rome the know-how faded, and the pigment dropped out of use until chemists reconstructed it in the 1800s.
Its strangest property was noticed only recently. Egyptian blue absorbs visible light and gives off strong, long-lasting infrared light, just past the red end of the spectrum: invisible to us, bright to an infrared camera. Conservators use it to find faded traces of blue on statues and walls that look unpainted, and it has turned up in places no one expected, including Raphael's 16th-century fresco The Triumph of Galatea.
It also corrects a myth. People in the ancient world made and traded a bright, stable blue, whatever their word lists say: Theophrastus called it kyanos. When Homer skips blue, it's a matter of vocabulary, not eyesight. Its modern cousins include cobalt blue, Prussian blue, synthetic ultramarine and the 2009 newcomer YInMn blue.
Swatches
- Egyptian blue · first synthetic pigment (approx.)
- Caeruleum · the Roman 'sky' name
Colors
Sources
- Museum of Fine Arts, Boston. Late Predynastic bowl from Hierakonpolis (identified by L. H. Corcoran).
- Vitruvius, De architectura, Book VII.
- Verri, G. (2009). The spatially resolved characterisation of Egyptian blue, Han blue and Han purple by photo-induced luminescence digital imaging. Analytical and Bioanalytical Chemistry 394: 1011–1021.
- Wikipedia, 'Egyptian blue'.
Hex values are screen approximations. Every page lists its sources.