Egyptian blue is the oldest synthetic pigment, produced by heating a mixture of silica sand, lime, copper and an alkali flux (soda or potash), and firing it in a kiln. The blue colour is due to the quartz. The pigment was first produced in Mesopotamia and Egypt in the 3rd millennium. In Minoan Crete, Egyptian blue was used to make beads and inlays, and as a fresco pigment.