|Organization or Institution||University of Florida|
Project Alchemy: EPR Spectroscopic Investigation of The Bologna Stone
Catherine Fabiano and Alex Angerhofer
Department of Chemistry, University of Florida, Gainesville FL 32611-7200, USA
The Bologna Stone is a barium sulfate (barite) derived luminescent compound of historical interest named for the Italian city of Bologna. Baryte is a common mineral found in many locations. However, the persistent luminescence after calcination and UV irradiation was historically only observed with stones found at Monte Paderno in Bologna, Italy. Previously lost in time, the secret of making the Bologna Stone Recipe has been rediscovered in the modern era.1 Part of the secret was the realization that the luminescence is strongly dependent on the presence of trace amounts of transition metal ions in the stone. Copper in a narrow concentration window is necessary, and the luminescence is quenched entirely by the presence of iron. This is attributed to Cu(I) filling a vacancy in the mineral which is transformed into BaS after calcination. EPR spectroscopic evidence indicates there is also Mn(II) present within the baryte. Current efforts are focused on elucidating the mechanism that causes this luminescence.
(1) Principe, L. M. Chymical Exotica in the Seventeenth Century, or, How to Make the Bologna Stone. Ambix 2016, 63 (2), 118–144.