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Insight into framework destruction in ultramarine pigments
Eleonora Del Federico1, Wolfgang Shöfberger, Johannes Schelvis
1Department of Mathematics and Science, Pratt Institute, 200 Willoughby Ave, Brooklyn, New York 11205, USA.
Inorganic Chemistry
|January 31, 2006
Summary
Ultramarine pigment fading involves sodalite framework destruction, releasing paramagnetic chromophores. This degradation is linked to changes in pigment color and structure, confirmed by spectroscopy.
Area of Science:
- Materials Science
- Chemistry
- Art Conservation Science
Background:
- Ultramarine pigments are susceptible to color fading.
- The exact mechanism of fading, particularly the role of the pigment's framework, is not fully understood.
Purpose of the Study:
- To investigate the structural changes in ultramarine pigments during color fading.
- To identify the chromophores responsible for color and their relationship to framework degradation.
Main Methods:
- Analysis of faded ultramarine pigments from a fresco environment and artificially faded samples.
- Utilized solid-state resonance-Raman spectroscopy, colorimetry, and solid-state 29Si and 27Al NMR spectroscopy.
Main Results:
- Sodalite framework destruction releases paramagnetic chromophores (S3(-*)) leading to pigment degradation.
- Fading in acidic media also causes framework destruction, beta-cage damage, and hydrogen sulfide (H2S) release.
- NMR parameters correlate with Raman signals of chromophores and colorimetric data (L*, C*).
Conclusions:
- Framework destruction is a key process in ultramarine pigment color fading.
- Spectroscopic and colorimetric data provide insights into the degradation pathways and chromophore behavior.