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

Egyptian blue, the oldest man-made blue ever, invented by the Egyptians around 5000 years ago has newly raised to prominence for its very recent finding on Raphael's Roman fresco the Triumph of Galatea hosted in Villa Farnesina, Rome. This is the first case in the Renaissance after centuries of oblivion. In recent years, due to its peculiar spectroscopic properties, Egyptian blue made itself known for manifold application in numerous and very different fields, far beyond its original purpose. Contrary to its brilliant present, its past remains still obscure, characterized from twists and turns which sporadically let it re-emerge. To track its modifications over centuries and places and piece together its fascinating path which has led it from pyramids to nanoscale applications, a network called BLUENET has been established. It is composed by more than 60 institutions and more than 100 researchers working on this subject and exploiting different aspects of Egyptian blue, from synthesis and its modifications to energetic, medical and forensic applications. A mini-review is given here accounting for the structural properties of such material, its currently applications in medical, forensic, energetics, and the raising questions reawakened by the authors' finding on the Raphael's fresco of Villa Farnesina together with their approach to address such issues by establishing a dedicated network composed by researchers from all over the world.