Visualization of vermilion degradation using pump-probe microscopy.

ABSTRACT: Here, we demonstrate the use of pump-probe microscopy for high-resolution studies of vermilion degradation. Vermilion (mostly ?-HgS), an important red pigment used in historical paintings, blackens over time, and metallic Hg and ?-HgS have been implicated as possible degradation products. Conventional analysis techniques have trouble differentiating ?- and ?-HgS with sufficiently high spatial resolution. However, pump-probe microscopy can differentiate metallic mercury, ?- and ?-HgS, and map each distribution on the microscopic scale. We studied artificial degradation of ?-HgS; femtosecond-pulsed laser irradiation induces an irreversible phase shift of ?- to ?-HgS, in which the initial presence of ?-HgS grains can increase the rate of conversion in their vicinity. Continuous ultraviolet exposure instead generates both liquid Hg and ?-HgS, with a conversion rate that increases with elevated temperatures. Last, we reveal the presence of ?-HgS as a natural degradation product in discolored vermilion layers in a 14th century Italian painting.

SUBMITTER: Yu J 

PROVIDER: S-EPMC6588381 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature