Visualization of vermilion degradation using pump-probe microscopy

Jin Yu; Warren S Warren; Martin C Fischer

doi:10.1126/sciadv.aaw3136

Visualization of vermilion degradation using pump-probe microscopy

Sci Adv. 2019 Jun 21;5(6):eaaw3136. doi: 10.1126/sciadv.aaw3136. eCollection 2019 Jun.

Authors

Jin Yu¹, Warren S Warren^{1

2

3

4}, Martin C Fischer^{1

4}

Affiliations

¹ Department of Chemistry, Duke University, Durham, NC 27708, USA.
² Departments of Radiology, Duke University, Durham, NC 27710, USA.
³ Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA.
⁴ Department of Physics, Duke University, Durham, NC 27708, USA.

Abstract

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