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Lead white is the most ancient and common white pigment used in muralpaintings. However, it tends to blacken with time due to its oxidation toplattnerite (\b{eta}-PbO2). Chemical treatments were used but they can put thepictorial layers supports at risks. Hereby we address the possibility ofthermally reconverting black plattnerite to white lead carbonates via amassicot (\b{eta}-PbO) intermediate, with a view to developing a restorationprocedure using continuous wave laser heating. We first investigated theconditions (temperature, time, and environment) in which pure powders react,before studying mural painting samples. Experiments were made in ovens and TGAand XRD and SEM characterization were achieved. Litharge ({\alpha}-PbO) andmassicot were obtained from plattnerite respectively between 564 and 567{\deg}C and at 650 {\deg}C. Lead carbonates (cerussite, hydrocerussite andplumbonacrite) formed from massicot in wet CO2 below 100 {\deg}C in a fewhours. Lastly, when heating plattnerite based mural painting samples, leadspecies reacted with binders and mortar, yielding massicot, plumbonacrite butalso lead silicate and calcium lead oxides. This demonstrates the viability ofthermal reconversion of darkened lead in mural, while raising concerns aboutthe formation of several lead species by reaction with mural paintingconstituents.

Thermal Reconversion of Oxidised Lead White in Mural Paintings via a Massicot Intermediate