Bio‐Inspired Fluorescent Calcium Sulfate for the Conservation of Gypsum Plasterwork

Abstract In this work, the potential of bio‐inspired strategies for the synthesis of calcium sulfate (CaSO ₄ ·nH ₂ O) materials for heritage conservation is explored. For this, a nonclassical multi‐step crystallization mechanism to understand the effect of calcein– a fluorescent chelating agent with a high affinity for divalent cations— on the nucleation and growth of calcium sulfate phases is proposed. Moving from the nano‐ to the macro‐scale, this strategy sets the basis for the design and production of fluorescent nano‐bassanite ( NB‐C ; CaSO ₄ ·0.5H ₂ O), with application as a fully compatible consolidant for the conservation of historic plasterwork. Once applied to gypsum (CaSO ₄ ·2H ₂ O) plaster specimens, cementation upon hydration of nano‐bassanite results in a significant increase in mechanical strength, while intracrystalline occlusion of calcein in newly‐formed gypsum cement improves its weathering resistance. Furthermore, under UV irradiation, the luminescence produced by calcein molecules occluded in gypsum crystals formed upon nano‐bassanite hydration allows the easy identification of the newly deposited consolidant within the treated gypsum plaster without altering the substrate's appearance.