Reconstructing a medieval recipe for red lead (Pb₃O₄): an archaeometry approach

Abstract

Red lead (Pb₃O₄), or minium, was one of the most common pigments in medieval manuscript illumination. However, the exact procedures used for its preparation and the thermal pathways underlying its formation remain insufficiently documented. In this study, we experimentally reconstructed a medieval synthesis of red lead based on recipes from Theophilus’s 12th-century treatise. Controlled transformation rate thermal analysis (CRTA) combined with in situ X-ray diffraction provided insights into the phase transitions occurring during heating. Our results indicate that the pigment referred to as “minium” in historical sources does not always correspond to pure Pb₃O₄, but may involve mixtures of PbCO₃, PbCO₃·2PbO, α-PbO, and β-PbO, depending on the thermal and atmospheric conditions. This variability reflects both the metastability of Pb₃O₄ and the technological diversity of historical lead-based pigments. By bridging experimental archaeology, historical reconstruction, and advanced materials characterization, this work contributes to a better understanding of medieval pigment production and its underlying chemical mechanisms. It highlights how archaeometry approaches can illuminate the interplay between craft knowledge and material science in the Middle Ages.