The colour blue was associated by the ancient Egyptians with figures of divinities. When it came to wall paintings depicting the gods the artists experienced some difficulty. Black, brown, yellow and red pigments existed prolifically in nature, but blue ones were rare. Only the scarce lapis lazuli, which did not occur nearer than Afghanistan, was known, and it did not lend itself to pigment manufacture, being of the wrong crystalline form.
The Egyptians therefore had to develop a blue pigment of their own devising, based upon copper. Sir Humphry Davy, analysing a blue glaze obtained in 1814 from the ruins of Pompeii, detected sand, lime and some form of copper. Later, the French geologist Fouqué discovered that the pigment concerned was essentially calcium copper silicate. Details of its manufacture had always been jealously guarded, but it was believed that desert sand, crushed limestone, natron and fragments of bronze or copper were fused into a glaze at temperatures between 850C and 1,000C and then ground into a powder. Various shades of blue resulted, all of them remarkably durable over the centuries.
Lucas, in his 'Ancient Egyptian materials and industry' (3rd ed, 1948) comments that the blue pigment principally used in Egypt was indeed a calcium copper silicate, manufactured by fusing silica, calcium carbonate, natron and in all probability native malachite, and grinding the product. According to comments by Stephanie Pain in New Scientist for January 22, the celebrated Egyptian blue was probably not invented in Egypt at all, but was brought from Syria or Mesopotamia and adopted by the Egyptian artists.