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“Identification by Raman spectroscopy of pararealgar as a starting material in the synthesis of amorphous arsenic sulfide pigments”. Vermeulen M, Saverwyns S, Coudray A, Janssens K, Sanyova J, Dyes and pigments 149, 290 (2018). http://doi.org/10.1016/J.DYEPIG.2017.10.009
Abstract: In this study, a combination of elemental analytical techniques (MA-XRF and SEM-EDX) were used to localize arsenic sulfide pigments within a 17th-century Dutch painting and in the stratigraphy of an 18th-century Flemish polychrome sculpture. Once located, Raman spectroscopy was used to obtain the vibrational signature of the arsenic sulfide pigments employed. By means of the latter analytical technique and due to the very distinctive Raman scattering signal of the various arsenic sulfide compounds, it was possible to identify the arsenic-based pigments as natural orpiment and amorphous arsenic sulfide. In the latter case, based on the minor bands observed and the good condition of the paint layers, it was possible to identify pararealgar, the orangey-yellow to yellow degradation product of realgar, as the initial arsenic sulfide material used for the synthesis of the amorphous pigment. To the best of our knowledge, this is the first time that combined pararealgar/amorphous arsenic sulfide Raman spectra are reported in historical samples. Therefore, this would be the first identification of pararealgar as the starting material to produce amorphous, arsenic sulfide pigments used in artworks.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.473
Times cited: 7
DOI: 10.1016/J.DYEPIG.2017.10.009
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“Photodegradation mechanisms and kinetics of Eosin-Y in oxic and anoxic conditions”. Alvarez-Martin A, Trashin S, Cuykx M, Covaci A, De Wael K, Janssens K, Dyes and pigments 145, 376 (2017). http://doi.org/10.1016/J.DYEPIG.2017.06.031
Abstract: Lakes based on Eosin-Y are extensively used by 19th century artists. Unfortunately, the identification of these pigments in paintings is a difficult task because Eosin-Y degrades very fast under the influence of light. The characterization of the (photo)degradation products of Eosin-Y can be very useful for the identification of these pigments in historic works of art and related cultural heritage artifacts. Furthermore, knowledge on how different factors influence the discoloration process (e.g. different types of irradiation sources and presence/absence of oxygen) is a valuable tool for preventive conservation. To this aim we performed a study on the photodegradation of Eosin-Y in solution under different illumination and in both oxic and anoxic conditions. The photodegradation of Eosin-Y was monitored by UV-VIS spectrophotometry, LC-QTOFMS and electrochemistry techniques. Results indicated higher degradation rates, by a factor of 20 or higher, under illumination with wavelengths near to the main absorbance band of the red pigment. Two different degradation pathways are observed under the conditions studied. LC-QTOFMS and electrochemistry suggested that in the presence of oxygen the degradation mechanism is an oxidative process where the breakdown of the structure causes the total discoloration. Meanwhile under anoxic conditions, a debromination process takes place while the chromophore, and consequently the color of the molecule in solution, remains essentially intact.
Keywords: A1 Journal article; Pharmacology. Therapy; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Toxicological Centre
Impact Factor: 3.473
Times cited: 18
DOI: 10.1016/J.DYEPIG.2017.06.031
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“Understanding the (in)stability of semiconductor pigments by a thermodynamic approach”. Anaf W, Schalm O, Janssens K, De Wael K, Dyes and pigments 113, 409 (2015). http://doi.org/10.1016/J.DYEPIG.2014.09.015
Abstract: Several artists pigments are semiconductors. Some of these materials appear stable over time, whereas others already show remarkable signs of degradation after limited time periods. The (in)stability of these pigments can be understood using a thermodynamic approach. For several pigment-related materials, the thermodynamic oxidation and reduction potential (ϕox and ϕred) were determined and evaluated considering the absolute energy positions of the valence and conduction band edges and the water redox potentials. The positions of ϕox and ϕred can be used in a fast screening of the stability of semiconductor pigments towards photoinduced corrosion in an aqueous/humid environment. This theoretical approach corresponds well with experimental data on pigment permanence and degradation phenomena found in literature.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Antwerp Cultural Heritage Sciences (ARCHES)
Impact Factor: 3.473
Times cited: 14
DOI: 10.1016/J.DYEPIG.2014.09.015
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“Geranium lake pigments : the role of the synthesis on the structure and composition”. Beltran V, Marchetti A, De Meyer S, Nuyts G, De Wael K, Dyes And Pigments 189, 109260 (2021). http://doi.org/10.1016/J.DYEPIG.2021.109260
Abstract: Eosin Y has an extraordinary capacity to form complexes with metallic elements, that have applications in many different fields, from photovoltaics and photocatalysis to historical artists? pigments. To unravel the complexes reactivity, it is essential to have a precise knowledge of their structure and composition, as well as how these can be affected by the synthesis protocol, an often underestimated factor. This manuscript presents a thorough investigation of the structure and composition of eosin Y complexes based on Al and Pb, by FTIR, XRPD and Raman spectroscopy, with a particular focus on the effect of the synthesis conditions. Results clearly show the change of the coordination mode in Pb complexes depending on the protocol, while the structure of Al complexes remains stable. In both cases, the formation of by-products was observed. Additionally, a detailed band assignment of the FTIR and Raman spectra of eosin Y and Pb and Al complexes is described, providing interesting details such as the interaction between the metallic ion and the xanthene moiety (chromophore). This is extremely important for the analysis of historical paintings where eosin Y is bonded to metallic ions, as well as for other materials in dye-sensitized solar cells, wastewater treatment or photocatalysis.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.473
DOI: 10.1016/J.DYEPIG.2021.109260
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