What is "egyptian blue"

Egyptian blue, also known as calcium copper silicate (CaCuSiO or CaOCuO(SiO)) or cuprorivaite, is a pigment used in ancient Egypt for thousands of years. It is considered to be the first synthetic pigment. The pigment was known to the Romans by the name caeruleum. After the Roman era, Egyptian blue fell from use and the manner of its creation was forgotten.

The ancient Egyptian word wadjet signifies blue, blue-green, and green.

The first recorded use of 'Egyptian blue' as a color name in English was in 1809.