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