Applications of Raman spectroscopy in art and archaeology

Abstract

The seventh edition of the International Congress on the Application of Raman Spectroscopy in Art and Archeology (RAA 2013) was held in Ljubljana (Slovenia) from 2 to 6 September 2013, with five plenary lectures, 40 oral presentations and 60 poster presentations. The number of active participants was 135 delegates from 32 countries among the 379 authors that presented at least one work. The use of Raman spectroscopy for identifying and studying the material component of the objects of art and antiquities has flourished in recent years. The increasing importance of the application of Raman spectroscopy in art and archeology is illustrated by an increasing number of research papers published each year and by the scientific conferences and sessions that have been dedicated to this research area in the past. One of the most important events dedicated to this subject today is the biennial International Congress on the Application of Raman Spectroscopy in Art and Archaeology (RAA). The RAA conferences promote Raman spectroscopy and play an important role in the increasing field of its application in Art and Archaeology. These prominent international events have a long tradition. Previously, they were held in London (2001),1 Ghent (2003),2 Paris (2005),3 Modena (2007),4 Bilbao (2009)5 and Parma (2011).6 The seventh edition of the International Congress on the Application of Raman Spectroscopy in Art and Archeology (RAA 2013) was held in Ljubljana (Slovenia) from 2 to 6 September 2013. As in the previous editions, the scientific program was focused on the characterisation of materials (pigments, inks, photographic material, gemstones, stones, precious stones, glass, ceramics, etc.), conservation issues affecting cultural heritage (decaying, corrosion, etc.), surface-enhanced Raman spectroscopy (dyes, organic pigments, etc.), Raman spectroscopy of biological and organic materials (resins, fibers, ancient organic compounds, etc.), Raman spectroscopy in paleontology and paleoenvironment, new Raman instrumentation and Forensic applications in art and archaeology (e.g. falsification). These studies were presented along 5 plenary lectures, 40 oral presentations and 60 poster presentations. The number of active participants was 135 delegates from 32 countries among the 379 authors that presented at least one work to the congress. At this point, we would like to mention Howell Gweynne M. Edwards, one of the ‘fathers’ of Raman spectroscopy applications to art and archaeology. Edwards retired in the year of the RAA 2013 edition, and it was an honour to host him in Ljubljana. The scientific and organizing committees acknowledged his lifetime work and gave him the stage to open the conference with an extremely interesting keynote lecture entitled Raman Spectroscopy of Extremophilic Biodeterioration: An Interface between Archaeology and the Preservation of Cultural Heritage. We believe that there is not a single scientist working in the field who would not have used at least one of his numerous publications for building the knowledge or as a good reference. Because of the increasing need for well defined and quickly available reference spectra, the congress was completed by a special session and round table about the most important criteria and requirements for the building of a public database of standard Raman spectra of compounds related to cultural heritage and archaeology, presented by Infrared and Raman Users Group (IRUG) members, in order to give a contribution to the building of the large, public, database of Raman spectra related to art, archaeology and conservation science by IRUG. The RAA 2013 edition takes pride in the general comment of the participants: ‘a very high scientific quality of the contributions’, 44 of them are collected in this special issue, ordered in the different topics suggested to participants when this edition was announced. Raman spectra of the new gemstone pezzottaite [Cs(Be2Li) Al2Si6O18] and Cs-beryl were studied and compared by Lambruschi et al.7 The extended Raman spectrum of pezzottaite was reported for the first time. Characteristic peaks were identified in the region of fundamental H2O stretching vibrations: Pezzottaite showed two weak Raman modes while beryl exhibits a single intense band. The position of H2O bands also allowed identification of the orientation of H2O into the channels (i.e. type I or II), assigning type II for pezzottaite. Furthermore, to complement the Raman data, other diagnostic methods were used, such as electron microprobe analysis in wavelength dispersive mode, laser ablation inductively coupled plasma mass spectrometry and single-crystal X-ray diffraction (XRD) characterisation. On the basis of the study, the authors proposed a protocol to distinguish between beryl and pezzottaite by Raman spectroscopy. Jeršek and Kramar8 reported on the Raman investigation of a baroque chalice made in 1732, one of the most richly decorated chalices in Slovenia, containing 456 embedded gemstones. In addition to the Raman data, gemology microscopy and ultraviolet fluorescence were used. The investigation showed the composition of the gemstones, identifying 24 diamonds, 93 rubies, 4 sapphires, 152 emeralds, 101 almandine garnets, 6 grossular garnets, 68 amethysts, 6 citrines, one specimen of glass and one of agate. Interestingly, the yellow-orange gemstones, so far identified as citrines, were determined as grossular garnets. Furthermore, on the basis of identified inclusions and in combination with macroscopic observations and literature data, the origin of the gemstones, as well as the substitutes for the lost stones, were determined. The Raman microspectroscopy results of the study of plasterwork decorations, located on the stalactite vaults of the Hall of the Kings in the Alhambra (Granada, Spain), were presented by Dominguez-Vidal et al.9 Field investigations were first carried out in situ (portable Raman spectrometer at 785 nm). Then, a well-directed sampling, based on the results obtained, was performed. Finally, more information was obtained on that reduced number of samples by means of laboratory studies. Almost all the pigments present in the decorations of the hall were identified by in situ Raman microscopy: cinnabar, minium, carbon black, natural lapis lazuli and synthetic ultramarine blue. However, the identification of blue-greenish and green pigments had to be performed on microsamples using a Raman microscope (excitation at 514 nm) revealing the presence of azurite (and its degradation compound clinoatacamite) and copper chlorides mixed with a small amount of lapis lazuli for green decorations. The stratigraphic study of the layers discovered the presence of redecorations with overlaying layers of pigments even of different colours. Nineteen natural specimens of azurite from European mining locations (exploited in medieval times) were analysed by Aru et al.10 using Raman microscopy to investigate the existence and identify the impurities. Malachite, hematite, goethite, cuprite, rutile and anatase were detected in a significant proportion of the specimens. Other minerals, detected less frequently, include quartz, calcite, cerussite, orthoclase, beudantite and jarosite. The most important finding was the nature of the black and orange-brown mineral grains; the classical assumption that such impurities in azurite pigments are mainly copper oxides (cuprite and tenorite) is partially incorrect as the orange-brown particles actually correspond to the iron oxides, goethite and hematite. These findings indicate that any iron oxides and malachite detected as minor impurities in azurite-containing museum objects should be taken as a consequence of the natural makeup of azurite specimens used for the pigments rather than a deliberate addition by the artist. Micro-Raman spectroscopy and optical microscopy under visible and ultraviolet light were applied by Pięta et al.11 to characterise the pigments, state of conservation and painting techniques used in the 17th century Golden Age panel painting ‘Servilius Appius’ (located at the Gdańsk History Museum), attributed to Isaac van den Blocke. 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was also The presence of such be when such objects have to be and should be to et studied a precious discovered in the at the in (Slovenia) to using optical and Raman microscopy to information about the used, as well as to identify the The optical microscope the use of a layers of were on a by one single of The pigments applied were all of and cinnabar, type I and carbon The identification of the type I of in this painting of the century is of a high importance it was that it on the in the first of the and type I are very in in Slovenia, the even more black and of were as a of degradation of Raman with was used by et to investigate the and materials as well as the degradation affecting the painting of the in compounds were identified and from materials used in recent and as information was used to the to laboratory Raman and in an to the degradation The use of the and as well as such as and and with and that the of the the of between and and the of the compounds were detected in the of 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