Green and blue pigments in Roman wall paintings: A challenge for Raman spectroscopy

This work demonstrates terahertz time-domain spectroscopy in reflection configuration on a class of inorganic and mineral pigments. The technique is validated for pictorial materials against the limitations imposed by the back-reflection of the THz signal, such as weak signal intensity, multiple signal losses and distortion, as well as the current scarce databases. This work provides a detailed description of the experimental procedure and method used for the determination of material absorption coefficient of a group of ten pigments known to be used in ancient frescoes – Cu-based (azurite, malachite, and Egyptian blue), Pb-based (minium and massicot), Fe-based (iron oxide yellow, dark ochre, hematite and Pompeii red) pigments and mercury sulphide (cinnabar) – and classified the vibrational modes of the molecular oxides and sulphides for material identification. The results of this work showed that the mild signal in reflection configuration does not limit the application of terahertz time-domain spectroscopy on inorganic and mineral pigments as long as (i) the THz signal is normalised with a highly reflective reference sample, (ii) the secondary reflected signals from inner interfaces are removed with a filtering procedure and (iii) the limitations at high frequencies imposed by the dynamic range of the instrument are considered. Under these assumptions, we were able to differentiate molecular phases of the same metal and identify azurite, Egyptian blue, minium and cinnabar, isolating the molecular vibrations up to 125 cm<sup>-1</sup>. The established approach demonstrated to be reliable, and it can be extended for the study of other materials, well beyond the reach of the heritage domain.

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“…The peaks at 363 cm −1 and at 201 cm −1 generated by Cu–O and Ca–O vibrations were not detected. 1,39,40…”

Section: Resultsmentioning

confidence: 99%

Terahertz Time-Domain Spectroscopy in Reflection Configuration for Inorganic and Mineral Pigment Identification

Artesani

Lamuraglia

Menegazzo³

et al. 2022

Appl Spectrosc

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“…Their chemical composition, K(Al,Fe III )(Fe II ,Mg)O 10 (OH) 2 , varies with ionic substitution. The Raman spectrum of the green samples was carried out to differentiate between these two very similar minerals [45]. The bands for glauconite and celadonite are described in the literature [46].…”

Section: Greenmentioning

confidence: 99%

Archaeological and Archaeometric Insights into a Roman Wall Painting Assemblage from the Blanes Dump (Mérida)

Castillo Alcántara,

Cosano Hidalgo,

Fernández Díaz

et al. 2024

Heritage

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In this paper we describe the archaeological and archaeometric analysis of a Third Pompeian Style assemblage from the Blanes dump in Mérida (Spain). Based on the pottery context, the material would have been part of the decoration of a public or private space remodelled towards the end of the 1st century AD. Several samples from to the middle area of the assemblage, including panels, inter-panels and a frieze, were selected and studied using X-ray diffraction (XRD), X-ray fluorescence (XRF), Raman, gas chromatography and petrographic analysis. The results revealed the use of hematite, cinnabar, minium and goethite in different panels, as well as goethite, Egyptian blue, calcite, glauconite and carbon for the decorative motifs. They allowed us to define the painting techniques used and how they have affected the degradation of the pigments.

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“…Looking at the relationship between the violet areas and the decorative motif, it is plausible that violet had been deliberately obtained with specific mixtures that give back a violet shade, where hematite is associated with both pyrolusite and Fe-Mn spinel. Traditional noninvasive and nondestructive Raman and XRF methods are not always straightforward for the investigation and characterization of green and blue pigments [97][98][99]. The combination of SR-XRD and SR-µXRF data may provide insight.…”

Section: Looking At Pigment Grains: Stratigraphies or Mixtures Of Hues?mentioning

confidence: 99%

X-ray Synchrotron Radiation to Look at Pigments in Antiquities: Overview and Examples

Gianoncelli,

Schöder,

Plaisier

et al. 2024

Heritage

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The recent upgrading of synchrotron radiation (SR) sources has favored, in the last few years, the construction and design of beamlines optimized for the study of cultural heritage materials, which may require ad hoc setups, specific spatial resolutions, and detection limits. In the field of cultural heritage, integrated approaches combining different techniques are often required, even at large facilities, where some beamlines offer the possibility of performing different types of measurements at the same point of analysis, complementing preliminary information usually obtained by conventional laboratory and/or portable in situ methods. An overview of the last ten years of synchrotron applications for the study of pigments is given, with discussion of upstream and downstream challenges to methods and techniques. The possibilities offered by the synchrotron techniques are illustrated by a case study of a particular class of painted ceramics, as an example of different research questions that are solved by a combination of SR-based methods.

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Green and blue pigments in Roman wall paintings: A challenge for Raman spectroscopy

Cited by 19 publications

References 33 publications

Terahertz Time-Domain Spectroscopy in Reflection Configuration for Inorganic and Mineral Pigment Identification

Terahertz Time-Domain Spectroscopy in Reflection Configuration for Inorganic and Mineral Pigment Identification

Archaeological and Archaeometric Insights into a Roman Wall Painting Assemblage from the Blanes Dump (Mérida)

X-ray Synchrotron Radiation to Look at Pigments in Antiquities: Overview and Examples

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