Publication Date:
2017-04-04
Description:
Red Pompeian paintings, very famous for their deep
intensity, are currently suffering from darkening. The
origins of this darkening degradation are not clearly
identified yet and remain a major issue for curators. In
the specific case of cinnabar (HgS)-based red pigment, a
photoinduced conversion into black metacinnabar is
usually suspected. This work is focused on the blackening
of red cinnabar paintings coated on a sparry calcite
mortar. Different samples exhibiting different levels of
degradation were selected upon visual observations and
analyzed by synchrotron-based microanalytical techniques.
Atomic and molecular compositions of the different
debased regions revealed two possible degradation
mechanisms. On one hand, micro X-ray fluorescence
elemental maps show peculiar distributions of chlorine
and sulfur. On the other hand, X-ray absorption spectroscopy
performed at both Cl and S K-edges confirms the
presence of characteristic degradation products: (i) Hg-
Cl compounds (e.g., corderoite, calomel, and terlinguaite),
which may result from the reaction with exogenous
NaCl, in gray areas; (ii) gypsum, produced by the
calcite sulfation, in black coatings. Metacinnabar is never
detected. Finally, a cross section was analyzed to map the
in-depth alteration gradient. Reduced and oxidized sulfur
distributions reveal that the sulfated black coating consists
of a 5-ím-thick layer covering intact cinnabar.
Description:
Published
Description:
7484-7492
Description:
reserved
Keywords:
Microspectroscopy Analysis
;
05. General::05.09. Miscellaneous::05.09.99. General or miscellaneous
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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