An evergreen blue. Spectroscopic properties of Egyptian blue from pyramids to Raphael, and beyond

•Thanks to its structure Egyptian blue is a multi-purpose material.•Recent application go far beyond its original vocation as a pigment.•Differently from its recent applications Egyptian blue past is quite mysterious.•The recent finding of Egyptian blue on Raphael’s Galatea re-awakened the interest for it after centuries of oblivion.•A dedicated network called BLUENET has been established for reconstructing the Egyptian blue changing fortunes over time.