Radiocarbon Dating of Magnesian Mortars: The Case of San Salvatore Church in Massino Visconti, Piedmont, Italy

This study presents a comprehensive analysis and radiocarbon dating of historical mortar and plaster samples from the San Salvatore—Massino Visconti complex in Piedmont, Northern Italy. Mortar samples and one charcoal sample were collected from various areas within the complex’s lower chapels. Samples were selected and characterized by means of a multi-analytical approach in order to draw inferences about their compositional, mineralogical, and microstructural features. The identification of hydromagnesite and magnesite in the mortar samples suggests the usage of magnesian binder mortar, potentially affecting radiocarbon dating due to its slower carbonation kinetics when compared to calcitic mortars. To mitigate this effect, a purification method was developed involving thermal treatment at 550 °C to isolate datable binding fractions. The results yielded reliable radiocarbon ages consistent with historical context, shedding light on construction materials dating from the 12th to 16th centuries. The study also challenges previous notions by demonstrating the feasibility of radiocarbon dating for magnesian mortars, opening new perspectives for dating such materials. These findings offer valuable insights into the construction history and material composition of the complex, corroborating historical information.