A Possible Natural and Inexpensive Substitute for Lapis Lazuli in the Frederick II Era: The Finding of Haüyne in Blue Lead-Tin Glazed Pottery from Melfi Castle (Italy)

The blue colour of glass and ceramic glazes produced in Apulia and Basilicata (Southern Italy) between the 13th and 14th centuries and connected to the Norman-Swabian emperor Frederick II, has been for long time under archaeometric investigation. It is usually associated to the em-ployment of lapis lazuli, due to the finding of the polysulphide blue chromophores typical of lazurite. On the other hand, the observation that the mineral haüyne, belonging to sodalite group as well as lazurite, can be blue and/or can gain the blue colour due to the same chromophores, when heated, questioned this automatic attribution, also considering that the mineral is charac-teristic of the rock haüynophyre of Melfi (Potenza, Southern Italy), location interested by the glass and pottery findings. In this paper, for the first time, several haüyne crystals were found in the blue glaze of a ceramic dish found at Melfi Castle, leading to the hypothesis that, in this case, the local haüyne-bearing source could have been used as coloring raw material. The discovery was possible thanks to SEM-EDS and Raman analyses that respectively highlighted the typical nu-merous presence of very fine sulphur-based inclusions in the crystals, and the characteristic Raman signal of blue haüyne. The study was focused also on the composition of the crystals in-clusions, aided by SEM-EDS and Raman maps, since the original very fine pyrrhotite was trans-formed into Cu and Pb phases (copper sulphates, copper sulphides and lead oxide) due to the reaction with cations that have mobilized from the glaze, while the migration of Si from the glass allowed the transformation of the rim of the haüyne, silica-undersaturated mineral, into a corona of euhedral and neomorphic little Pb-rich-feldspars, a silica-saturated phase.