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Sulfur K-edge micro- and full-field XANES identify marker for preparation method of ultramarine pigment from lapis lazuli in historical paints

2020; American Association for the Advancement of Science; Volume: 6; Issue: 18 Linguagem: Inglês

10.1126/sciadv.aay8782

2375-2548

Alessa A. Gambardella, Marine Cotte, Wout De Nolf, Kokkie Schnetz, Rob Erdmann, Roel van Elsas, Víctor González, Arie Wallert, Piet D. Iedema, Myriam Eveno, Katrien Keune,

Pigment Synthesis and Properties

Ultramarine blue pigment, one of the most valued natural artist's pigments, historically was prepared from lapis lazuli rock following various treatments; however, little is understood about why or how to distinguish such a posteriori on paintings. X-ray absorption near-edge structure spectroscopy at the sulfur K-edge in microbeam and full-field modes (analyzed with nonnegative matrix factorization) is used to monitor the changes in the sulfur species within lazurite following one such historically relevant treatment: heating of lapis lazuli before extracting lazurite. Sulfur signatures in lazurite show dependence on the heat treatment of lapis lazuli from which it is derived. Peaks attributed to contributions from the trisulfur radical-responsible for the blue color of lazurite-increase in relative intensity with heat treatment paralleled by an intensified blue hue. Matching spectra were identified on lazurite particles from five historical paint samples, providing a marker for artists' pigments that had been extracted from heat-treated lapis lazuli.