Spectroscopic Properties of Inorganic and Organometallic Compounds: Volume 40 (Specialist Periodical Reports - Spectroscopic Properties of Inorganic and Organometallic Compounds) - Hardcover

Hardcover

ISBN 10: 1847559182 ISBN 13: 9781847559180

Publisher: Royal Society of Chemistry, 2009

Synopsis

Reflecting the growing volume of published work in this field, researchers will find this book an invaluable source of information on current methods and applications.

About this title

About the Author

Professor Jack Yarwood is an emeritus professor at Sheffield Hallam University. Professor Simon Duckett is a research group leader at the University of York, UK. His group is mainly involved in the design, development and implementation of NMR methods, supported by the synthesis of inorganic and organometallic complexes. Dr Richard Douthwaite is at the University of York, UK. His main research interests include molecular and materials chemistry and photocatalysis. Both an EPSRC college member and fellow of the Royal Society of Chemistry, Dr DOuthwaite is also on the SCI National Materials Committee.

Excerpt. © Reprinted by permission. All rights reserved.

Spectroscopic Properties of Inorganic and Organometallic Compounds

Techniques, Materials and Applications Volume 40

By J. Yarwood, R. Douthwaite, S. B. Duckett

The Royal Society of Chemistry

Copyright © 2009 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-84755-918-0

Contents

Preface Jack Yarwood, Richard Douthwaite and Simon B. Duckett, 15, 
Raman spectroscopy of inorganic materials in art and archaeology: spectroscopic analysis of historical mysteries Howell G. M. Edwards, 16, 
Spectroscopic properties and lattice dynamics of ferroelectric and related functional oxide ceramics Jan Petzelt and Stanislav Kamba, 49, 
Raman spectroscopy of cementitious materials Leon Black, 72, 
Optical spectroscopy of silicates and glasses Philippe Colomban and Linda C. Prinsloo, 128, 
Optical spectroscopy of liquids in and near inorganic oxides John T. Fourkas, 150, 
Simulation of spectroscopic properties of inorganic compounds using modern modelling procedures Trevor J. Dines, 171, 
Photoelectron spectroscopy and quantum mechanical calculations of organometallic complexes Sergey Y. Ketkov, 216, 
Characterisation of photochemically formed reactive species from kinetic and thermodynamic data using UV-Vis. Laser flash photolysis, Time resolved IR and matrix isolation techniques Conor Long and Mary T. Pryce, 244, 
Gas-phase molecular structures determined by electron diffraction David W. H. Rankin and Heather E. Robertson, 272, 
Nuclear quadrupole resonance spectroscopy K. B. Dillon, 298, 
High pressure crystallography of inorganic and organometallic complexes Stephen A. Moggach and Simon Parsons, 324, 
Structure—function relationships and mechanistic pathways in homogeneous catalysis as probed by ENDOR spectroscopy Emma Carter and Damien M. Murphy, 355, 
Spectroscopic studies and reactions of corrosion products at surfaces and electrodes Marek Odziemkowski, 385, 

CHAPTER 1

Raman spectroscopy of inorganic materials in art and archaeology: spectroscopic analysis of historical mysteries

Howell G.M. Edwards DOI: 10.1039/b715002b

Introduction

The application of chemical analysis to art and archaeological specimens can be traced back to the late 18th and early 19th Century; in 1815, Sir Humphry Davy read a paper entitled 'Some experiments and observations on the colours used in painting by the Ancients' to the Royal Society and thereby probably laid claim to the first scientific publication in this field. Davy's analytical work comprised a study of the pigments on wall-paintings excavated at Pompeii and several palaces in Rome using classical wet chemical methods. In this paper, Davy refers to previous analytical studies made by savants, that had not been published hitherto but which had been communicated verbally to him, including Klaproth's discovery of cobalt in an ancient blue glass specimen, and tantalisingly refers to his minimal sampling of these precious archaeological specimens which were in the care of his friend, Canova. Hence, he recognised that the destructive sampling required for the provision of analytical chemical information using the standard methods of qualitative and quantitative analysis pertaining at that time, although undesirable, was nevertheless necessary for the provision of novel information about the chemical composition of the artefacts which was not accessible by other means.

The extent of the problem facing the analyst can be gauged from the classic studies of English porcelains carried out by Eccles and Rackham and by Church in the late 19th and early 20th Centuries, when whole items were consumed for the gravimetric determination of ceramic body compositions in attempts to classify the articles as belonging to certain factories — in this respect, the records of early porcelain factories of the composition of their wares was vital for the attribution of the specimens. It is not surprising, therefore, that the renaissance of chemical analysis applied to archaeological and art specimens has been driven in the last decade by the application of non-destructive spectroscopic micro-sampling techniques and this has reinforced the scientific authentication and provenancing of specimens as a central theme at the interface between history, art and science.

It is certainly true that most vibrational spectroscopic studies of art work and archaeological artefacts carried out up to the last quarter of the 20th Century was exclusively the preserve of the infrared spectroscopist; there are several reasons for this, but the most important are that earlier Raman spectroscopic instrumentation used Toronto mercury arc excitation, operating mainly at 435.8 nm, and photographic, or later, photoelectric recording. This required rather large quantities of pure samples that were stable to high-energy visible radiation and the total absence of fluorescence emission, which could swamp the much weaker Raman scattering intensity. In the late 1970s, however, the classic marriage of a laser Raman spectrometer with an optical microscope developed by Delhaye and Dhamelincourt, with sensitive detectors, revolutionised the scope of applications that could be undertaken using the new laser Raman microscopy, and almost immediately resulted in the first brief description of artefact analysis using this novel instrumentation. So it was that the first publications of Raman spectroscopic studies of materials relevant to art and archaeology appeared from the mid- 1980s, from Guineau and his collaborators in Paris. In a recent survey of the literature in the last decade which has addressed Raman spectroscopic applications to art and archaeology by Vandenabeele et al., the growth of the technique can be clearly seen expressed as a proportion of the total number of papers published in art and archaeology, and this is reflected in data presented in the Web of Science (Fig. 1), where a ten-fold increase in Raman papers published in art and archaeology between 1998 and 2007 should be noted.

Also, a greater awareness is now apparent across several disciplines at the arts/science boundaries, and particularly in the field of scientific conservation and restoration, because publications using the Raman spectroscopic technique for studying art works are now appearing in journals which hitherto had not attracted research work of this kind, for example, Studies in Conservation, J. Archaeological Science, Archaeometry, and Antiquity as well as in the more mainstream spectroscopic literature. The growth of work in the area of Raman spectroscopy applied to art and archaeology has stimulated the acquisition of spectroscopic instrumentation and trained specialists by museums and a new focus directed at the communication of the novel results forthcoming from these studies; this has itself generated a growth of specially themed topics at Raman spectroscopy conferences, such as ICORS and GeoRaman. A whole new conference series on the topic of Raman in Art and Archaeology(RAA), which started first as a one-day meeting in the British Museum in 2001 attended by 120 delegates from 17 countries, will attain RAA5 in Bilbao, Spain in a five-days meeting scheduled for 2009. Finally, the first book dedicated to the applications of Raman spectroscopy in art and archaeology appeared in 2005, published by the Royal Society of Chemistry, containing 25 chapters written by specialists working at this interface and covering a host of topics including, textiles, mummies, biomaterials, prehistoric art, dyes and pigments, wall paintings, frescoes, manuscripts ceramics, glass papyri and scrolls, jewellery, gemstones and jade.

The analytical information derived from optical, spectroscopic and diffraction experiments on artwork is being used increasingly to provide evidence for the authentication of high-value artwork in museum collections and in the private domain and also for the scientific provenancing of unknown artworks; the success of this approach is dependent upon the acquisition of data derived from the materials comprising the art object or artefact at the elemental and molecular levels.

Several key analytical techniques, of which Raman spectroscopy is one, are now recognized for their ability to provide microanalytical data from minute amounts of sample and from the totally non-destructive examination of specimens in situ. Other techniques in this class include PIXE-SEM, μXRF, FTIR and GC-MS, which have been combined with mRS (micro Raman spectroscopy) to generate data which are directly apportioned to discussions on the authenticity or otherwise of specimens of artwork; in particular, manuscripts, wall paintings, frescoes, easel paintings, statuary, gemstones and jewellery, and ivories have been analysed and the spectroscopic results interpreted on the basis of a composition of minerals, dyes, pigments and resins which were known to have been in artistic use at the time of creating of the artwork or artefact. Hence, scientific provenancing has now been accepted as a rigorous exercise in the forensic examination of artworks. For example, the identification of Prussian blue, a pigment whose synthesis was first reported in 1704, on a manuscript or artefact purporting to be from the 17th Century or earlier would give rise to some serious questions about the authenticity of the artwork; this has been superbly demonstrated by the detailed work of Burgio and Clark, who following their Raman studies of papyri artefacts purporting to be from ancient Egyptian archaeological sources and some 3000 years old concluded from the presence of synthetic mineral pigments and associated dyes that the papyri were more correctly placed in the 20th Century! Tables 1-8, taken from an earlier review by Clark present a timeline for the commonly accepted usage of mineral pigments and associated materials in ancient art work; whereas in early mediaeval or Renaissance art, the pigments available to artists were normally mineral in origin, with some exceptions such as verdigris, mosaic gold and lead-tin yellow, as synthetic chemistry was born out of alchemy, a wider range of pigments became available for artistic evaluation.

Hence, the synthesis of Prussian blue in 1704, which has already been mentioned above, and lead chromate in 1809 provide defining start dates in recorded history for the use of these pigments in art — they could not have been used before these dates and their presence in an earlier art work would result in serious debate about the authenticity of the art work or artefact. The discovery of aniline and azo dyes in the late 19th Century gave rise to a whole new palette for the Impressionist and post-Impressionist painters, providing them with a novel range of vibrant colours.

What is perhaps not generally realised in studies of early pigments is the adoption of technologies for production or conversion of materials that have often gone unrecorded. For example, the use of carbon (charcoal or bone black), pararealgar, and red ochre in wall paintings and artefacts all have synthetic roots in prehistory. What must also be appreciated is that the pigments that were used in early art works were derived mainly from natural mineral sources and hence were prone to contamination and compositional variability; hence, associated minerals from the surrounding rock matrix are expected to occur in the powdered pigment extracts. In addition, the presence of quartz signatures in the Raman spectrum of a mineral pigment is often indicative of the use of fine-grained river sand to aid the grinding process in the preparation of the pigment for art work. Other pigments of indefinite composition which can be related to their method of production are verdigris (basic copper carbonate), Egyptian blue (a copper silicate), hydrocerussite (basic lead carbonate) and St. John's white (calcium oxide/ hydroxide/carbonate).

Some major principles which form the basis of the Raman spectroscopic analysis of archaeological artefacts and artwork (Fig. 2) are worthy of further examination; the most important of these are outlined below:

• In situ or microsampling is highly favoured among exponents of the spectroscopic methods of analysis for artwork provenancing: although this is in itself admirable, it does raise a problem which lies at the heart of most analytical experiments and procedures, namely, is the analysis of perhaps ng or pg of material in a laser beam focus truly representative of an object which may have a mass of several kg and is probably heterogeneous? Nevertheless, the microsampling of an easel painting which involves the application of a "swabbing" technique in which literally miniscule amounts of pigment are removed from a painting by the application of a dry cotton bud, the adhering particles of pigment on which are then subjected to micro-Raman analysis is very much favoured.

• Spectroscopic analysis provides qualitative, and possibly quantitative, information about the molecular composition of the materials comprising the artwork; this "hard" information is then compared with what may have been expected from an artwork of the expected historical period. It is the latter "soft" science comparison which provides a potential flaw in the conclusions which will then be drawn since historical opinion about materials used by an artist at a particular time is based on known recipes or manuscripts. There is strong evidence that for the former, artists could be deliberately misleading about their pigments, for example as found from the Raman spectroscopic analysis reported by Derbyshire and Withnall, of the 16th Century 'Armada Jewel' of Nicholas Hilliard, which was created in 1588 for Queen Elizabeth to celebrate the defeat of the Spanish Armada sent by King Philip II of Spain to invade Britain. It appears from the spectroscopic analysis that Hilliard, a much-respected limnologist and miniaturist to the Court of Queen Elizabeth, deceived his contemporaries in the use of mineral pigments in his palette and did not in fact use the pigments recommended in his published recipes. In the case of manuscripts, the situation can often be tenuous for a different reason; mosaic gold, tin(IV) sulfide, was found during the Raman spectroscopic studies undertaken upon a 13th Century polychrome statue of Santa Ana from the monastery of Santa Maria la Real, Silos, Spain (Fig. 3).

The problem here is that a manuscript in a Naples scriptorium dating from the 14th Century is the first to mention the use of mosaic gold as a pigment in Europe — some 100 years after the Santa Ana statue was made and decorated. Does this mean that per se the statue is therefore a fake? It should, however, be recognised that there are Chinese manuscripts which report the manufacture and usage of of mosaic gold in their alchemical literature which predate the Neapolitan manuscript by some 1500 years! The burnishing of the mosaic gold to form a bright metallic finish on the stone substrate is also related very closely to the underlying pigment composition of the statue as we have reported in a recent paper, yet this process had not been reported historically hitherto. This illustrates very well the gap in our historical knowledge of technological achievements in antiquity and the role that spectroscopy can play in the interpretation of the methodologies of pigment production. In this case, the spectroscopic analysis has suggested the presence of an ancient, long lost processing and materials technology hitherto unsuspected by archaeologists and art historians in which the tin(IV) sulfide was applied directly over a ground layer of mercury(II) sulphide and burnished to form an amalgamated tin mirror finish. We shall see further examples of this aspect of information retrieval from spectroscopic data that exceeds the mere identification of inorganic and organic materials, however important that is for the scientific analysis and attribution of art works to specific periods. It is appropriate here to present in the form of a spectral stackplot (Fig. 4), the Raman spectral data of tin(IV) sulphide, mercury(II) sulfide and lead(II) lead(IV) oxide minerals, mosaic gold, cinnabar and minium, respectively, which show the key features used in the spectroscopic discrimination between these pigments, all of which were used in antiquity. It should be noted that in these minerals the major vibrational spectroscopic bands occur at wavenumbers below 400 cm" and, therefore, are not usually accessible using conventional laboratory infrared spectrometers. Also in Fig. 4, can be seen the Raman spectrum obtained from the golden hem of the dress of Santa Ana — clearly showing the presence of all three mineral components illustrated above; gold itself is an atomic metal and does not possess a Raman vibrational spectrum.

• The identification of a specific pigment for comparison with a published recipe or artist's palette is an established method for scientific restoration and attribution of art works; the Raman spectroscopist must be aware of several pitfalls in art history, where either the pigment nomenclature is vague or, worse, where the chemical description of a pigment changes with time yet the pigment nomenclature in published manuscripts or treatises remains the same! An example of the former is Naples yellow, which has been generally assumed to be di-lead antimonate, Pb2 (SbO4) 2Naples yellow! Further nomenclature problems are created with the mineral pigments which are used in antiquity, such as mercury(II) sulfide (cinnabar), HgS, known to the Romans as minium. Minium secondarium was reserved for red lead (lead tetroxide), Pb3O4. Even in Roman times the term minium was applied to red lead and similarly to mixtures of red lead and cinnabar. By the Renaissance period, however, minium was applied to red lead pigment alone, and a new term, red ore of lead, was given to the mineral crocoite, lead chromate, PbCrO4.

(Continues...)

Excerpted from Spectroscopic Properties of Inorganic and Organometallic Compounds by J. Yarwood, R. Douthwaite, S. B. Duckett. Copyright © 2009 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2009
• Language: English
• ISBN 10: 1847559182
• ISBN 13: 9781847559180
• Binding: Hardcover
• Number of pages: 449
• Editor: Jack Yarwood