title: Insight into framework destruction in ultramarine pigments.
abstract: We report key evidence on the framework destruction in ultramarine pigments upon color fading. Experiments on faded pigments in a fresco painting environment reveal that the paramagnetic chromophores are set free via sodalite framework destruction and are subsequently degraded. Fading in acidic media produces similar results, although a larger number of beta-cages appear to be destroyed, and H2S is released. The findings are further supported by studies on natural and synthetic ultramarine pigments of various shades via solid-state resonance-Raman spectroscopy, colorimentry, and solid-state 29Si and 27Al NMR spectroscopy. NMR parameters are shown to correlate well with the intensities of Raman signals corresponding to the S3(-*) chromophores. A further correlation is established between the colorimetric parameters, L* (lightness) and C* (chroma), and the paramagnetic shift and paramagnetic linebroadening in NMR spectra for both 27Al and 29Si.
authors.affiliation: Department of Mathematics and Science, Pratt Institute, 200 Willoughby Ave, Brooklyn, New York 11205, USA.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Del Federico
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Shöfberger
authors.forename: Johannes
authors.initials: J
authors.lastname: Schelvis
authors.forename: Sofia
authors.initials: S
authors.lastname: Kapetanaki
authors.forename: Lindsey
authors.initials: L
authors.lastname: Tyne
authors.forename: Alexej
authors.initials: A
authors.lastname: Jerschow