Degradation Process of
Lead Chromate in Paintings
by Vincent van Gogh Studied by Means of Spectromicroscopic Methods.
3. Synthesis, Characterization, and Detection of Different Crystal
Forms of the Chrome Yellow Pigment
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Abstract
The painter, Vincent van Gogh, and some of his contemporaries
frequently
made use of the pigment chrome yellow that is known to show a tendency
toward darkening. This pigment may correspond to various chemical
compounds such as PbCrO<sub>4</sub> and PbCr<sub>1‑<i>x</i></sub>S<sub><i>x</i></sub>O<sub>4</sub>, that may each
be present in various crystallographic forms with different tendencies
toward degradation. Investigations by X-ray diffraction (XRD), mid-Fourier
Transform infrared (FTIR), and Raman instruments (benchtop and portable)
and synchrotron radiation-based micro-XRD and X-ray absorption near
edge structure spectroscopy performed on oil-paint models, prepared
with in-house synthesized PbCrO<sub>4</sub> and PbCr<sub>1‑<i>x</i></sub>S<sub><i>x</i></sub>O<sub>4</sub>, permitted
us to characterize the spectroscopic features of the various forms.
On the basis of these results, an extended study has been carried
out on historic paint tubes and on embedded paint microsamples taken
from yellow-orange/pale yellow areas of 12 Van Gogh paintings, demonstrating
that Van Gogh effectively made use of different chrome
yellow types. This conclusion was also confirmed by in situ mid-FTIR
investigations on Van Gogh’s <i>Portrait of Gauguin</i> (Van Gogh Museum, Amsterdam)