16402120 COST G8 Benefits of NonDestructive Analytical Techniques for Conservation

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COST Action G8

Benefits of non-destructive analytical

techniques for conservation

Papers from a COST Action G8 workshop held

in Kalkara, Malta, on 8 January 2004

Edited by

Annemie Adriaens, Christian Degrigny

and JoAnn Cassar

COSTEuropean cooperation in the field of

scientific and technical research

2005 EUR 21636 EN


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COST Action G8 Benefits of non-destructive analytical techniques for conservation.

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Table of Contents

1 COST Action G8: Non-destructive analysis and testing of museum objects 5Annemie Adriaens

2 The philosophy of the workshop 9JoAnn Cassar and Christian Degrigny

3 Documentation in relation to non-destructive analysis in conservation 13Claude Borg

4 Non-destructive X-ray analytical techniques for art and archaeology 21Manfred Schreiner, Bernadette Frhmann and Dubravka Jembrih-Simbrger

5 Material analysis in architectural paint research and restoration ofwall paintings 33

Mads Christian Christensen

6 Assessment of building conservation needs - the value of a

non-destructive approach 43George Ballard

7 Non-destructive investigation of art objects: some case studies 45Marie Soares, Erwin Hildbrand, Peter Wyer, Eberhard Lehmann, Peter Vontobel,

Stephan Hartmann and Eckhard Deschler-Erb

8 Non-destructive investigation of works of art using portable XRFand high energyPIXE/PIGE 51

Martina Griesser, Andrea Denker, Ariadna Mendoza, Elke Oberthaler,Roswitha Denk, Jrg Opitz-Coutureau and Andrzej Markowicz


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9 The Guarrazar treasure (Toledo, Spain). Visigothic goldwork andgemstones of the 7thcentury 59Alicia Perea, Thomas Calligaro, Guy Demortier, Jean-Claude Dran

and Ignacio Montero

10 Radiocarbon-dating by accelerator mass spectrometry:fundamentals and applications toarchaeology 69

Lucio Calcagnile, Gianluca Quarta and Marisa DElia

11 Non-destructive analytical tools at the Centre for Research and Restorationof theMuseums of France: present status and future trends 77Thomas Calligaro, Jean-Claude Dran and Joseph Salomon

12 The importance of X-Ray Fluorescence (XRF) techniques for thecompositional analysisof museum objects 87

Bogdan Constantinescu

13 Opportunities for SR- and neutron-based non-destructive analysisof museum objects 89

Emmanuel Pantos

14 Use of Prompt Gamma Activation Analysis (PGAA) for the non-destructive

investigation of archaeological artefacts 91Zsolt Kasztovszky, Zsolt Rvay and Gbor L. Molnr

15 Preventive ion beam inspection of glass treasures 99Christian Neelmeijer and Michael Mder

16 Checking rapidly the surface and bulk heterogeneity of metallicarchaeological samples by combined non-destructive IBA methods in anon-vacuum geometry 109

Guy Demortier

17 Qumran and the Dead Sea scrolls: a jigsaw puzzle 111Jan Gunneweg, Jan Wouters and Marta Balla


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1 COST Action G8: Non-destructive analysis and

testing of museum objects

Annemie Adriaens

Abstract COST Action G8 (2001-2006) aims at creating a Europe-wide network that would enable co-operation and interaction be-

tween two groups of professionals: people directly concerned with the maintenance of our cultural heritage - conservators, curators, arthistorians, archaeologists - and analytical scientists, including chemists, physicists, geologists, metallurgists, mineralogists and micro-biologists. The main objective of the action is to improve the preservation and conservation of our cultural heritage by increasing avail-able information on museum objects through non-destructive analysis and testing. The scientific activities of COSTAction G8 includeorganising short-term scientific missions to train scientists from both groups in the others field as well as to transfer practical experi-ence among the European countries. Regular meetings in the form of workshops are organised in order to exchange the acquiredknowledge within a broader group; six working groups are currently active, which allow close collaboration in a specific field.

Keywords COST Action G8, cultural heritage, non-destructive analysis

Introduction

The conservation and preservation of our cultural heritage has become one of the main concerns within Europetoday. In particular, the increasing need for non-destructive investigations is a major issue, as sampling is inmost cases restricted in view of the value or the uniqueness of the object. Even in cases that allow sampling,non-destructive testing offers the possibility of obtaining more information from one specific sample, as com-plementary techniques may be applied.

In the analytical sciences, many non-destructive techniques are available, such as ion beam analysis, autoradi-ography and optical spectroscopy, all of which can, in principle, be used in this field. Museums, however, donot always have access to these techniques, while many of the necessary research instruments and analyticalfacilities are located in specialised research institutes, as they require very specific expertise. Some techniquesmay still need to be introduced and established in the field of cultural heritage.

It is for these reasons that COST Action G8 has been established, which aims at creating an environment thatenables co-operation and interaction between museums and natural scientists. COST is an intergovernmentalframework for European co-operation in the field of scientific and technical research, allowing the co-ordina-tion on a European level of nationally funded research projects (http://cost.cordis.lu/src/home.cfm).

Objective and benefits

The main objective of COST Action G8 is to improve the preservation and conservation of our cultural herit-age by increasing available information on museum objects through non-destructive analysis and testing. Thisis accomplished by creating a Europe-wide environment, in which people directly concerned with the mainte-

nance of our cultural heritage (ie art historians, archaeologists, conservators and curators) and analyticalscientists (ie physicists, chemists, material scientists, geologists, etc.) can exchange information.


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A 50/50% balance between the activities of both groups is aimed at, which should result in greater interest. Theexpected benefits are twofold. First, the capability of answering questions related to museum objects, whichcannot be readily solved now, will be enhanced. This includes the exchange of information on available non-destructive techniques and the requirements for performing investigations on valuable or unique objects. Inaddition, museums and similar institutes will have easy access to universities and research facilities that pro-

vide such techniques.

The first successful step in this direction has been provided by COSTAction G1 (1995-2000). The focus of thisaction was confined to the use of Ion Beam Analysis (IBA) for art and archaeological objects. This techniquewas applied to various archaeological objects, such as paint layers, pottery, glass, enamels, obsidian, stone,tools, bronzes, coins and gold jewellery (Respaldiza 1997; Demortier 2000). The expansion to a multidiscipli-nary community and the use of additional non-destructive techniques allows researchers to obtain furthercomplementary information.

The scientific programme

COST Action G8 has three main scientific activities. The first one includes organising short-term scientificmissions between participating institutions. The goal of these STSM (5 days 2 months) involves the trainingof scientists from both professional groups in the others field, as well as the transfer of practical experienceamong European countries. Priority here is especially given to young researchers.

Secondly, regular meetings in the form of workshops are organised, often in collaboration with museums andconservation institutes, to exchange obtained information in a broader group, to discuss new themes, and tobuild interest and create possibilities for new collaborations (Townsend et al. 2003).

The goals of both activities are listed in detail in Table 1.1.

Short term scientific missions Workshops

- train scientists of both professional groupsin the others field as well as transferpractical experience between theEuropean countries,

- address specific problems concerningmuseum objects as well as collect andcompare data,

- compare the use of standing facilities andportable equipment,

- exploit the advantages and limitations ofthe different techniques also incomparison to techniques commonly usedtoday in the field of cultural heritage,

- art historians, archaeologists andconservators obtain easier access toanalytical research instruments.

- exchange (obtained) information in abroader group,

- prove the non-destructive properties of thetechniques,

- build interest and give the possibility ofnew collaborations,

- assist in choosing the method(s) bestsuited for a specific problem.

Table 1.1Scientific goals of short-term scientific missions and workshops.


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Apart from the yearly workshops and STSM between participating groups, separate working groups have beencreated. The working groups allow a close collaboration and an extended and efficient exchange of knowledgewithin a specific topic, and therefore a more efficient way of publishing the obtained results. The followingthemes are addressed:

Technology and authenticity, involving the identification of the materials and their production techniques.Within this working group two distinct but related topics are studied: (1) the investigation and verificationof ancient recipes starting from the Mesopotamian and Egyptian texts up to the 19th century books of tech-nology including descriptions of how craftsmen prepared and made their products are made available and(2) the authentication of art and archaeological objects, ie the identification of fakes.

Origin and provenance, including the characterisation and location of natural sources of the raw materialsused to make (museum) objects. The main goal is to contribute to establishing patterns of raw materialprocurement, trade or exchange.

Degradation processes, corrosion, weathering. This working group deals with the problem of alteration ofmuseum objects and the way non-destructive techniques can be used to measure this damage or monitor itwith time.

Preservation and conservation. The working group is concerned with the treatment of works of art in orderto slow down deterioration, the identification of the nature and extent of damage, the assessment of thecauses of deterioration. Work in this field also implies the control of the environment in which the object islocated, such as monitoring of the temperature, relative humidity and lighting, ensuring proper storage, sup-port and security.

Development of analysis procedures involving three main goals: (1) the use and improvement of truly non-invasive techniques (they do not require a sample to be removed from the object), (2) the maximization ofinformation and minimization of consumed volume when a sample must be removed and (3) the develop-ment of portable / mobile equipment so that monitoring can be done on site.

Biological and Material Culture of Qumran at the Dead Sea. This working group deals with three aspectsof the study of material remains at Qumran, ie the biological and the material cultural ones and the conser-vation of this cultural heritage.

COST Action G8 started in February 2001 and will run for five years. At the time of writing, twenty-one Eu-ropean countries had joined. They are listed in Table 1.2.

Austria Germany Poland

Belgium Greece Romania

Bulgaria Hungary Slovakia

Czech Republic Israel Slovenia

Denmark Italy Spain

Finland Malta Switzerland

France Netherlands United Kingdom

Table 1.2Participating countries (June 2004).


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Further information

For further details and information about the possibility of joining the Action, please contact the author orvisit our web site at http://srs.dl.ac.uk/arch/cost-g8.

References

Demortier, G. and Adriaens, A. (eds) 2000.Ion Beam Study of Art and Archaeological Objects, Luxembourg:Office for Official Publications of the European Commission.

Respaliza, M.A. and Gomez-Camacho, J. (eds) 1997.Applications of Ion Beam Analysis Techniques to Artsand Archaeometry, Seville: Secretariado de Publicaciones de la Universidad de Sevilla.

Townsend, J., Eremin, K. and Adriaens, A. (eds) 2003. Conservation Science 2002, London: Archetype Publi-cations.

Authors address

Annemie Adriaens, Ghent University, Department of Analytical Chemistry, Krijgslaan 281-S12, 9000 Ghent,Belgium ([email protected])


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2 The philosophy of the workshop

JoAnn Cassar and Christian Degrigny

Introduction

The use of analytical techniques to enhance the understanding of conservation issues is recognised as a prior-ity by all specialists working in the field of conservation of our cultural heritage. However, the lack of equip-ment and training in some institutions often prevents this principle from being respected. Research institutesequipped with sophisticated analytical tools can most certainly perform non-destructive analysis, as opposedto less well-equipped conservation laboratories and conservation training schools. The latter institutions are,above all, expected to be more conscious of the ethical issues involved, in view of the delicate role they playin the training of new generations of conservators; however their limited budget does not usually allow themto purchase expensive equipment. Nowadays, the tendency is to correct this unacceptable situation throughimproved collaboration among specialists. In this respect, COST Action G8 plays a very important role. Dur-ing the workshop on Non-destructive analytical techniques for conservation, organised in Malta in January2004, the speakers, who came from museums as well as conservation and research institutions from thirteendifferent European countries, demonstrated how the gaps between research laboratories and professionals in-volved in the conservation of our cultural heritage are being bridged.

This publication presents the numerous contributions presented during this specialised meeting. In order torespect the design of the original workshop, the contributions of all speakers are presented in these proceed-ings. Wherever the full paper was unavailable, the abstract given to the participants during the workshop ishere being reproduced.

Most of the speakers, many of whom are research scientists, tended to use the term non-destructive to char-acterise the types of analyses they are carrying out. Conservation professionals, however, will generally referto these methods, where no sample is taken, as being non-invasive. This distinction is of particular impor-tance in the conservation field, as in this way, one of the most important ethical principles is respected. Theterm non-destructive investigation, on the other hand, will normally include also the study of samples thatcan be re-used for further examination.

Three approaches of how professionals can benefit from non-destructive and/or non-invasive analytical tech-niques were presented during this workshop. Training in such analytical techniques in conservation schoolswas considered first, followed by how these techniques are utilized in conservation laboratories working onmuseum artefacts, or during on-site investigations of built structures. Finally, the recent interest of researchlaboratories was discussed.

The role of conservation schools

During their training, conservation students learn to respect specific codes of ethics. The preferred use of non-invasive and/or non-destructive analytical techniques is one of them. The tools used (X-ray radiography, Infra-

red reflectography and UV fluorescence photography being the most common ones) may not be the most so-phisticated, but through them, ethical principles are passed on to the students and other professionals involved


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in conservation projects. In this light, the role of the educator is essential, and he/she has to keep constantlyup-to-date with the latest developments in this field. Furthermore, those entrusted with the training of conser-vators,must clearly explain the benefits and limitations of each analytical method, to promote satisfactorily itsappropriate use. This is ably illustrated by Borg who, in his paper, writes how up-to-date knowledge in thedocumentation field is passed on to conservation students at the Malta Centre for Restoration through on-site

exercises. Schreineret al. demonstrate, on the other hand, how the teaching of non-invasive X-ray analyticaltechniques within the programme of conservation/restoration at the Academy of Fine Art in Vienna contributesto the regular use of these methods by new generations of recently trained conservators.

The role of conservation laboratories

Conservation laboratories, working either through cultural heritage institutions or else independently, shouldapply, as far as possible, the most recent non-invasive and/or non-destructive analytical techniques to studyartefacts. For this reason, these laboratories are usually well equipped with sophisticated tools suitable for thepurpose. Occasionally, these laboratories also develop their own analytical protocol, as described by Chris-tensen working at the National Museum of Denmark. Here, a specially developed sampling device, combined

with low-vacuum SEM-EDS and micro-Raman spectroscopy, allow for the non-destructive examination ofsamples of architectural paint layers. On the other hand, it is often possible for conservation laboratories to usemore selective analytical tools, through the establishment of collaboration agreements with research centres.This cooperation is described in two papers, one by Soares et al. working at the Swiss National Museum inZrich and another by Griesseret al. working at the Kunsthistorisches Museum in Vienna, Austria. Both theseinstitutes work closely with scientific research institutions either in their own country or elsewhere. The mainobjective in these cases is to apply non-destructive and/or non-invasive tools to help solve art history and/orconservation issues. These analytical tools are clearly regarded as a complement to destructive investigations(such as embedded cross-sections from paintings or metal samples) since they allow for the examination ofmany different areas. Indeed, detailed analytical data obtained from a limited number of analyses of cross-sec-tions can thus be confirmed without further sampling.

Conservation laboratories necessitate the participation of a multidisciplinary team composed of experts com-ing from different backgrounds, and which is usually inclusive of art historians, curators, conservators, archae-ologists, scientists and/or architects. Such a composite team is able to study the artefact from all possible an-gles to then reach agreement on its documentation and/or a solution or solutions to any conservation problem.This aspect is perfectly illustrated in the paper by Perea et al., where it is explained how the Visigoth Guar-razartreasure has been examined by international teams using different approaches based on non-invasiveand/or non-destructive analytical techniques.

It must be emphasised that conservation professionals have a major role to play in the further development ofnon-invasive and non-destructive techniques. Without the precise expression of their needs, it will not be pos-sible to optimise the use of the existing tools. These professionals must work hand-in-hand with the researcherswho develop these techniques, in order to improve the quality of the information gathered from the artefact

with the minimum impact on it.

The role of research laboratories

Research laboratories in universities and research centres generally possess the most sophisticated and up-to-date equipment, in part due to their involvement in industrial projects. University staff is usually very special-ised, and often very keen to share knowledge. However, these scientists are often unaware of the specificproblems related to cultural heritage and the ethics which must be respected in the field, and they are at timesdifficult to approach. Furthermore, the majority of the projects carried out within these institutions are researchoriented. These institutions rarely support analytical services that represent the actual needs of the conservationprofessionals. Another major problem is the need to transport the artefacts to the research laboratory. Collabo-

rative work between conservators and scientists is essential, as the latter group may lack the basic knowledgeon how to handle cultural heritage artefacts. Nonetheless, very important information is gained from these in-


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vestigations, and it is often thanks to these isolated studies that great improvements are made in the mode ofinvestigation of cultural heritage artefacts.

As a recent example of the contribution of research laboratories in the fields of archaeology and conservation,the paper presented by Calcagnile et al. discusses radiocarbon-dating by the newly set up Accelerator Mass

Spectrometer at the University of Lecce in Italy. Although complex, this technique has the advantage of reduc-ing sampling from artefacts to the minimum. It thus opens up new fields of application, such as the dating ofprecious, rare or very small artefacts. Another contribution by research laboratories is in the study of the prov-enance and the manufacturing process of artefacts. Here, Prompt Gamma Activation Analysis (PGAA) appearsto be quite a promising multi-element analytical technique, as Kasztovszkys paper illustrates. Here are pre-sented the potentials of this technique, as well as some case studies (on metal and stone).

Ion Beam Analysis (IBA) of museum artefacts has become a widespread means of investigation in many Euro-pean countries. Many conservation professionals have established partnerships with nuclear physicists, and worktoday as a team on several major conservation projects. Demortier is certainly one of the originators of the use ofthese techniques in the field of Cultural Heritage. In another paper, Calligaro et al., presents a thorough review ofthe potential of the accelerator facility (AGLAE) installed at the Centre for Research and Restoration of the Mu-

seums of France (C2RMF) at the Louvre. This accelerator, purposely dedicated to the study of artworks, givesessential information when non-invasive investigation is required. IBA include a vast array of applications. Neel-meijeret al.s paper presents a promising one: the use of PIXE (Particle Induced X-ray Emission) to study poten-tially vulnerable glass objects in museums and to help suggest appropriate preventive conservation strategies.

X-Ray Fluorescence is another commoner, cheaper and also very versatile method of non-destructive investi-gation of artworks, which can also be used in a non-invasive manner. However, as explained in Constantines-cus abstract, it is important that all necessary precautions are taken when using this method. It must alsohowever be emphasised that today the trend is to develop portable tools.

Other nuclear techniques offer possibilities of investigation that were not even imagined a few decades ago.This is the case for Synchrotron Radiation (SR) based analyses (micro-XRD), a technique discussed by Pantos.

Here the very high intensity of the beam and the small beam footprint allow for the rapid investigation of alarge number of micro-samples.

In another paper, this time by Gunneweg et al, the philosophy of this workshop is summarised through a casestudy which can be compared to a detective story. Through collaborative work between different specialists,and the use of some of the most sophisticated non-invasive and non-destructive analytical techniques (NAA,SR based analyses), it has become possible to answer some of the pending questions about the provenance ofthe Dead Sea Scrolls at Qumran, near the Dead Sea.

On-site analysis

Although the emphasis of the COST G8 Action is on the study of museum objects, the opportunity was takenduring this workshop to demonstrate also to Maltese professionals working in architectural conservation hownon-invasive and/or non-destructive analytical techniques can, and should, be applied to buildings and monu-ments; this is ably illustrated by the paper by Christensen and the abstract by Ballard. This, as well as the ap-plicability of such study methods to the evaluation of conservation problems associated with archaeologicalsites, as seen in the paper by Borg, was emphasised.

The use of non-invasive and/or non-destructive analytical techniques to enhance the understanding of conser-vation issues varies from one country to another. In this respect, another objective of this workshop was toprovide a level playing field, whereby the participants could share their different experiences. This was effec-tively done by a number of guest speakers who have benefited from Short Term Scientific Missions (STSM)within COST Actions G8 or G11 and who showed how positive these STSMs have been in improving interac-

tions between professionals in different European countries. This, it is felt, is the true value of the COST G8Action, as revealed by this specialised workshop and reflected in these proceedings.


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Authors addresses

JoAnn Cassar, Institute for Masonry and Construction Research, University of Malta, Msida MSD06, Malta,([email protected])

Christian Degrigny, Diagnostic Science Laboratories, Malta Centre for Restoration, Bighi, Kalkara, CSP 12,Malta ([email protected])

Endnotes

1 Ion beam study of art and archaeological objects


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3 Documentation in relation to non-destructive

analysis in conservation

Claude Borg

Abstract Documenting in two dimensions and three dimensions offers a lasting and faithful record that can be used by researchers,

students, conservators and the general public. Two dimensional and three dimensional models have a variety of applications. They maybe used as an important archive that can enable closer monitoring of artefacts or sites. Very accurate measurements can be made with-out the need of returning on site; it is also possible to plan the conservation/ restoration of the cultural heritage resource.

This paper presents the tools currently used by the Documentation Division at the Malta Centre for Restoration (MCR). The need ofappropriate training for their proper use has led MCR to establish a degree programme in heritage documentation. Research in the fieldis not neglected either at the Centre. One of the most promising techniques developed is Thealasermetry , an integrated system, basedon the accuracy of an electronic theodolite, and the technologies of laser scanning and photogrammetry, maximizing the data collectioncapacity of each instrument. This hybrid system overcomes limitations encountered when using solely photogrammetry or laser scan-ning.

Keywords documentation, cultural heritage, non-destructive, technology, education, research, hybrid surveying

Introduction

The Documentation Division at the Malta Centre for Restoration (MCR) works within a multi-disciplinary unitaiming at integrated conservation. The aim of the Documentation Division is to provide assistance to variousprofessionals in the field of conservation, including a comprehensive service to the Institute for ConservationStudies (the teaching arm of MCR), to the public, ecclesiastical and the private sectors in those projects involv-ing the documentation of artefacts, architectural and archaeological heritage.

The Division is involved in a number of tasks. These include two dimensional imaging and graphic documen-tation, three dimensional imaging, library and information studies and geographic reference system data inputand design.

Some of the other technologies used include the application of non-invasive investigations such as X-ray radi-ography, Infrared reflectography and UV fluorescence photography.

Technology

X-ray radiography as a non-invasive investigation tool is very interesting since the invisible light penetratingthe work of art reveals not only the initial ideas and afterthoughts of the artist or modifications beyond theartists control, but also the state of conservation of the artefact, enabling its authenticity to be easily recog-nized. Furthermore it is the most efficient means of showing whether additions were painted by the same or bya different hand from the rest of the picture. The settings of the instrument are important to obtain the best

contrast definition. Only a collection of a large number of radiographic documents makes it possible to seri-ously compare data and information (Gilardoni 1994).


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Given the longer wavelength of infrared, it is possible to penetrate paint layers on the surface and obtainreflections from underlying layers and therefore highlight preparatory drawings or pentimenti. The sensitiv-ity of the method is determined by the thickness and paint layer type. Using this light source, a wide range ofmaterials such as paints, adhesives, binders and pigments may be recognised and interpreted by conservatorsand/or art historians trained in reading these results (Gilardoni 1994). One may therefore obtain information

that is not detected with the naked eye. The Infrared reflected image may only be photographed in black andwhite or visualised on a monitor. In our case the latter is generally used.

Fluorescence is the excitation effect of some materials which, once struck with ultraviolet radiation with agiven frequency, re-emit secondary radiation of a greater wavelength. With this technique, the painting is zoneinspected with the purpose of highlighting, through the differentiation of the materials used, any restoration,re-painting or even forgery. The inspection must be carried out in the dark in order to have the ultra violetsource as the sole luminous source (Gilardoni 1994).

Other instruments used for documentation in relation to non-destructive analysis include laser scanning, thetotal station and photogrammetry. The most important feature of the three instruments is the fact that the ob-jects are measured without being touched. Therefore the term remote sensing is also used by some authors.

Principally, these instruments are used for object interpretation and object measurement.Photogrammetry is the technique of measuring objects from photogrammes. If an object is photographed fromtwo different positions, which are parallel to each other and at right angles to the object, the photogrammeshave then similar properties to the two images impinging on our retina. Therefore the overlapping area of thesetwo photographs, which are called a stereopair, can be seen in three dimensions, simulating mans stereo-scopic vision.

Various laser scanners exist on the market. These are usually categorised by their application in relation to thedistance from the artefact. Generally, lasers can be long range, medium range or surface. The laser scanningsystem records three dimensional co-ordinates that are presented as thousands or millions of points. These datacan be obtained by using more than one type of laser scanner (medium/long range). Multiple scans are takenfrom different viewpoints, creating a three dimensional mosaic of the object. These viewpoints are integratedtogether with the use of spheres or absolute co-ordinates that are included in every scan. The margin of errorof the instrument of up to 0.6mm can result in an error propagation1 with the consequence that the virtualmodel does not respect the true form.

The data acquired can be processed further by meshing through triangulation planes2, texture mapping3, seg-mentation and the gathering of detailed measurements allowing for the creation of sectional elevations andplans.

The total station records three dimensional co-ordinates. Similar to the laser scanner, it emits a laser beam. Itcan form a closed network (closed traverse). Once a traverse is formed, the total station can return to the samestation and further readings can be taken. As long as the station is identifiable, these readings may be takeneven years later.

Of the three instruments just mentioned, the laser provides the most surface detail; however it is limited whencollecting information on objects with defined outlines. Conversely, it is photogrammetry that allows the userto produce very accurate outlines in three dimensional polygons. Line drawing or points derived from the ster-eopairs can also be traced across the surface of the model; however, this is a long process and becomes dif-ficult along complex surfaces, such as eroded stone.

Lasers can be applied to various artefacts and structures. On average, it takes eight different scanning view-points with a medium range scanner to complete the model for example of a simple Majolica vase 50cm high,with plane surfaces. Had the model been more complex, additional scans would have been required. Themodel allows the mapping of all cracks and lacunae directly on a three-dimensional model in vector format.Figure 3.1 shows members of the Documentation Division of MCR using the Mensi GS100 long range scanner

on Salvatur Chapel, Kalkara, Malta, while Figure 3.2 shows the various scans that were merged into one, threedimensional model.


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The exterior of the chapel was scanned with a long range time of flight scanner4 while the interior was scannedprimarily with a medium range scanner which works by triangulation. The medium range scanner is more ac-curate and may achieve point to point accuracies of up to 0.6mm. In this example, this analytical tool was used

to gauge the wall thicknesses and the geometry of the chapel and how the thickness of the wall varies withheight. It is also a complete document as every stone was documented (in three dimensions) in the presentstate.

In the case of the prehistoric altar from Tarxien (Malta), housed at the Maltese National Museum of Archaeol-ogy, measurements were easily acquired from the three dimensional model. In this example, where it wasneeded to have an accuracy greater than 1mm point to point, a medium range scanner was used. The first image(Figure 3.3) shows the altar with the red spheres used for integrating the model. Figure 3.4 shows the side ofthe meshed image.

Figure 3.1 Members of theDocumentation Division using the

Mensi GS100 long range scanner onSalvatur Chapel.

Figure 3.2 Various scans of Salvatur Chapel, Kalkara, Malta takenusing the Mensi GS 100 long range scanner and that have been

consolidated into one three dimensional model.

Figure 3.3 Vue of the Tarxien altar currentlyconserved in the Museum of Archaeology, Valletta,

with the red spheres used for consolidation of themodel.

Figure 3.4Side view of

the samealtar scanned

with themedium

rangescanner.


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This system may also be applied to obtain other data such as the weight, intricate sectional contours at anyposition, and angles.

The prehistoric temples in Malta are some of the most complex sites to survey. The great morphological com-plexity and the intricate three-dimensional individual forms require a particular methodology to achieve a

highly accurate three-dimensional model. The model has various applications and may be used as a local geo-graphic information system model to map all data intrinsic to the monument by their exact location. The sur-rounding area of the temple site was scanned with a long range scanner while the intricate interiors werescanned with a medium-range scanner. The resulting model may also be an ideal tool for virtual reality pres-entations, structural analyses and monitoring the movement of individual megalithic elements. It is possible tomonitor and assess in a non-destructive way the rate of surface deterioration with the application of a surfacescanner, in addition to the other scanners. Owing to the large amount of data created by these high detailedscans, only sample areas are usually identified and mapped, giving an illustration of the surface deteriorationtaking place.

Education

Within the future academic programme of conservation/restoration at the Malta Centre for Restoration inMalta, the teaching of surveying and analytical techniques that can be used in a non-destructive way plays animportant role. For this reason, the Documentation Division has embarked on a two year traineeship. Thistraineeship is offered in a number of disciplines. These include photography, Computer Aided Design (Auto-CAD) including graphic documentation, laser scanning, photogrammetry and surveying. During this trainee-ship, the need to offer a degree course was identified. The Bachelor of Documentation Studies was developedtwo years ago to address the lacunae in the documentation field. The concept of the course lies in training stu-dents in the skills required for the whole documentation process, from data collection to data management. Thecourse presents the various approaches, philosophies and techniques which go into documenting cultural herit-age. The degree is interdisciplinary, providing students with a balance of theory and practice in informationtechnology. The student learns to assess what type of documentation is appropriate to a site or artefact; this will

depend on various factors, including the nature of the object or site, the purposes of the record and the culturalcontext. The course includes core study units that address the background information a student will need towork within the cultural heritage field; in addition, two dimensional documentation, three dimensional docu-mentation and the management of the data collected are also incorporated. Since the aim of the course is toproduce professionals who know how to use the various surveying and analytical tools, the available instru-ments can be used by the students during their practical work and fieldwork.

The course will offer the students multidisciplinary training. It will enable future graduates to work with abroad range of professionals within the cultural heritage field including conservators, museum curators, ar-chaeologists and conservation architects. Once trained, the documentation specialist should be able to recom-mend the most appropriate documentation strategy for recording different artefacts and sites and the archivingof the information thus obtained in an accessible format. The course leading to a Bachelor of Documentation

Studies should start in October 2005.

Research

The use of digital technology for measuring and recording three-dimensional shapes of great morphologicalcomplexity, as in the case of the prehistoric temples in Malta, offers a lasting and faithful record that can beused by future researchers. The Documentation Division has experimented on developments in 2D and 3Dsurveying. Of particular interest is Thealasermetry (Borg and Cannataci 2002, Borg and Magrin 2002; Borg etal. 2002). This is an integrated system, based on the accuracy of the theodolite and the technologies of laserscanning and photogrammetry, maximizing the data collection capacity of each instrument. The Malta Centrefor Restoration has applied this hybrid technique in a survey of one of the oldest free standing man-made struc-

tures extant in the world, the megalithic temples of Kordin III seen in Figure 3.5. This hybrid system results ina more cost-effective project than if the two systems of laser scanning and photogrammetry had been used


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independently. Above all, it overcomes limitations and metric error propagation which occur when using laserscanning and photogrammetry separately. This data acquisition and post-processing system satisfies a numberof requirements, ranging from site and engineering surveys to documenting historical buildings or monu-ments.

Figure 3.5 The oldest free standing man-made structures extant in the Mediterranean,the megalithic temples of Kordin III.

The theodolite registers three-dimensional co-ordinates and is the only tool that offers the possibility of main-taining overall precision by using a closed-network system. This data can be read up to an accuracy of 1mm.Being the most precise instrument of the three mentioned, the theodolite can provide the co-ordinates needed

to integrate all the data generated by the other surveying tools. However, the theodolite is not designed to cre-ate virtual surfaces and contours. In close range photogrammetry, digital cameras can offer the accuracyofanalogue cameras, although this depends on the resolution of the camera and the distance from the object.Therefore, this may be compensated for by shooting more digital stereopairs, and adding more control points.To control the orientation and integration of these extra stereo models, theodolite surveyed photo-control be-comes indispensable.

It has been demonstrated that how, by drawing on the strengths of these three systems, more accurate measure-ments and details can be recorded than when using one system alone. The theodolite co-ordinates are used asthe binding factor for the merging of all the data gathered from the three systems. Therefore, these co-ordinatesare used as the reference points for the control markers used for photogrammetry and laser scanning.

Using these co-ordinates to restitute the photogrammetric stereopairs, very accurate outline drawings can beobtained. The theodolites co-ordinates are taken as the first viewpoint. Using this system, the laser scanviewpoints can be integrated within the theodolites closed-network. The results obtained from the differentprocesses are merged into one system. This allows the triangulation of the laser scanning points to be modelledwithin the vector outlines estimated from the photogrammetric stereopairs.

The same photographs obtained by photogrammetry can be directly used for texture mapping of the integrateddata. Linking the photographs directly to the theodolite ensures that this process is done with the maximumaccuracy and ease possible. Figure 3.6 shows an example for Kordin temples. Overall, the expected object ac-curacy that can be achieved is of +/-1mm. Such a system provides an important archive which can enable bet-ter monitoring of such archaeological sites.

Although Thealasermetry is a highly accurate surveying system, it requires many different operators and is

costly. On the other hand, the mono laser is a method that fulfils a number of the functions ofThealaserm-etry, utilising less human resources and fewer instruments (Borg 2003). This is a system which can be used by


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Figure 3.6 Use of thealasermetry to survey the megalithic temples of Kordin III.

one individual alone. The Malta Centre for Restoration has applied both techniques in a survey of a barrelvault, at the Presidents summer residence in Verdala, Malta. The mono system resulted in a cost-effectivemethodology, but with a slightly lower accuracy than Thealasermetry. The mono laser system maximizes thefunctions of all the accessories within the laser scanner tool in the best manner possible. Although it is possibleto take digital photographs with an integrated camera, the resolution is lower than may desirable for texturemapping. A 5.5 multiplier lens to zoom in on smaller areas of the object being documented produces a photo-graph of much higher resolution. The laser is here used to simulate the total station methodology and so alsoovercomes the metric error propagation which usually results when using laser scanning in a traditional way.This data acquisition and post-processing system satisfies a number of requirements, ranging from site andengineering surveys to documenting historical buildings or monuments, in particular where the main require-ment is the ortho photography.

Conclusion

Documentation in relation to non-destructive analysis in conservation is very important in the further under-standing and documentation of cultural heritage. The ability to obtain valuable information from objects, assurface and subsurface data, without touching the work of art, proves that the application of these tools is in-dispensable. They are principally used for object interpretation, including type, quality, quantity and objectmeasurement together with form and size.

The training of the documentation specialist should prove to be an important asset within the multi-disciplinaryteam. The documentation results will address the direct needs of the conservator or conservation architectamong other specialists involved.

Using a laser scanner as part of a hybrid approach has truly complemented photogrammetry, but the level ofdevelopment of the technology to date does not enable laser scanning to replace photogrammetry completely,

due to the inaccuracies already indicated. It is not impossible however to foresee a level of development wherea hybrid approach such as Thealasermetry is made almost redundant by improvements in the laser scannerpackage.

Acknowledgements

Documentation Division, Malta Centre for Restoration, Bighi, Kalkara, Malta


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Endnotes

1 The propagation error means the addition of all the errors, which could amount to a large error at the end ofthe survey

2 Triangulation means forming a triangular two dimensional plane within three known three dimensional co-ordinates. The numerous triangular two dimensional planes form the three dimensional surface of themodel

3 Texture mapping means draping the photographs of the object over the 3D model

4 Time of flight scanners, measure the time taken for the light beam to leave and return. In this way, the dis-tance may be measured.

References

Borg, C.E and Cannataci, J. 2002. Thealasermetry: a hybrid approach to documentation of sites and arte-facts. CIPA at International workshop, Corfu, September 2002.

Borg, C.E. and Magrin, M. 2002.Long-range laser scanners: Moving towards a hybrid methodology or ahybrid tool?. In Proceedings of 3DiMENSIon Conference, Paris, October 2002.

Borg, C.E., Anastasi, A., Borg, I. et al. 2002 Using Mensis Technology for Restoration of Cultural Heritageand how to combine an S25 with a GS100. In Proceedings of 3DiMENSIon Conference, organized byMensi, Paris, October 2002.

Borg, C. 2003. Thealasermetry vs Mono Laser Systems: Comparative Results on Simple Curved Plains. InProceedings of ISPRS conference, Ancona, Italy, July 2003.

Gilardoni, A., Taccani Gilardoni, M., Ascani Orsini, A. et al. 1994.X-rays in Art, 2nd edition. Gilardoni publica-tion, Lecco, Italy.

Authors address

Claude Borg, Documentation Division, Malta Centre for Restoration, Bighi, Kalkara, Malta ([email protected])


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4 Non-destructive X-ray analytical techniques

for art and archaeology

Manfred Schreiner, Bernadette Frhmann and Dubravka Jembrih-Simbrger

Abstract An overview of the techniques used in art and archaeology is presented and the applicability of methods using X-ray radiation

such as X-ray radiography, X-Ray Fluorescence (XRF) and X-Ray Diffraction analysis (XRD) as tools for non-destructive investiga-tions of artefacts is discussed. X-ray radiography, for example, is a standard technique widely used and accepted by art historians, ar-chaeologists, curators and conservators as this method enables the gathering of information about the manufacturing process and thecondition of an object without touching the artefact. XRF and XRD enable non-destructive determination of the material compositionof artefacts and the determination of the crystalline structure of the components too. Air path systems and instruments with the micro-beam of X-ray and even synchrotron radiation were applied for the analysis of easel paintings, metallic artefacts, engravings as well aspigments in paint layers and glass objects.

Keywords X-ray radiography, X-ray fluorescence analysis, synchrotron X-ray micro-diffraction analysis, pigments, Art Nouveauglass

Introduction

At the present time particular collaboration is taking place between art and science and co-operation betweenscientists, archaeologists, art historians, curators and conservators seems fairly well established, as the applica-tion of analytical techniques, initially developed in the field of materials science, to objects of art and archaeol-ogy gives art historians and archaeologists the possibility to gain information about the material compositionof such objects and gives answers to the questions of where, when or even by whom such an artefact was made.Additionally, such investigations can help us to understand the way of manufacturing objects and hence theway of life of the cultures studied. Scientific investigations are also valuable, and in some cases indispensable,for conservation projects in order to differentiate the original parts of an object from later additions, formerrestoration works, falsifications or even fakes. Furthermore, our cultural heritage is doomed to disappear be-cause of ageing and the deleterious effects of environmental pollution. The degradation of monuments oroutdoor bronzes is well known, but all artefacts, even in exhibitions or well conditioned museums, libraries, orarchives are subject to deterioration. These phenomena must be studied extensively in order to understand the

kinetics of decay and to develop treatments and ways for preventing or slowing down these processes (Baerand Low 1982; Mairinger and Schreiner 1982; Vandiveretal. 1942; Jerem and Biro 2002; Van Grieken etal.2002)

For the systematic investigations of objects of art and archaeology, two complementary sources of informationare available. The holistic approach makes use of radiation from gamma-rays to infrared in order to generateimages of an object, which cannot be determined by the naked eye. These methods are in a strict sense non-destructive, which means that neither samples have to be taken from an object nor is the material of an artefactchanged during the investigations. This procedure accords well with the way an art historian, archaeologist orconservator would like to deal with works of art. Figure 4.1 shows, for example, the structure of an easel paint-ing with the support (canvas) and the different paint layers as well as the different penetration and hence infor-mation depths of UV, IR and X-ray radiation. As the UV-light is already absorbed by the uppermost layers,

generating the well known effect of UV-fluorescence, mainly retouches or later additions can be visualised bythis technique. Contrary to light in the visible range (390 780nm), IR radiation is usually not absorbed by


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most of the pigments and can penetrate the upper paint layers. Consequently, underdrawings (the concept of anartist) can be studied by means of IR-photography as well as the Vidicon-technique (Maringer 2003). Thecomplete package of the paint layers, which is characteristic of the artists creative process and the evolutionof a painting, can be visualised by using X-ray radiation. An external source emits X-rays, which are absorbedby the materials of an object according to their characteristic absorption properties, and the transmitted radia-

tion can be registered on a film or by other X-ray sensitive materials. The techniques of X-ray radiography aswell as computer tomography are standard tools widely used and accepted, as these methods enable informa-tion about the manufacturing process and the condition of an object to be obtained without touching the ar-tefact (Lang and Middleton 1997; Mairinger 2003).

Figure 4.1 Structure of an easel painting and penetrationdepths of radiations.

The second source of information, where the material composition of small areas is determined, consisted main-ly of chemical methods of analysis until World War II. Since the 1940s, many techniques based on physics havebeen developed and used extensively for elemental analysis. In some cases, even spectacular results, such as the

rediscovery of the composition of lead-tin yellow could be achieved, for example by optical emission spectros-copy. In the yellow parts of Dutch paintings of the 14th 17th centuries, Jacobi (Jacobi 1941) determined the ele-ments Pb and Sn. Systematic investigations at the Doerner Institute in Munich yielded the composition of Pb

2SnO

4,

a yellow pigment, which was used by the Dutch painters and replaced by Naples yellow (Pb(SbO3)

2or Pb

3(SbO

4)

2)

in European easel paintings after approximately 1750 (Kuehn 1993). However, as chemical and many instrumen-tal analytical techniques are destructive, and require small samples to be taken from an object, the application ofthese methods to objects of art and archaeology are severely limited nowadays. X-Ray Fluorescence (XRF) aswell as X-Ray Diffraction (XRD) analyses have gained growing interest in the last decades (Schreineretal. 2000;Mantleretal. 2000) as both methods have been proved to be sufficiently non-destructive, if used with care andrespect to possible damage due to extensive radiation doses.

It is the purpose of this contribution to present an overview of the application of X-ray radiography, XRD and

XRF to objects of art and archaeology and to present recent developments using a micro-beam for the non-destructive determination of the crystalline structure of pigments as well as the elemental composition of paint-ing materials and glass of the Art Nouveau manufactured by Tiffany/USA and Loetz/Austria at the end of the19th and beginning of the 20th centuries.

X-ray radiography

The collections of the Academy of Fine Arts in Vienna contain several paintings on canvas with views of Ven-ice (veduta = city views) painted by the famous Venetian painter Francesco Guardi (1712 1793). He was theyounger son of Paolo Guardi, who was a famous painter too, as was his elder brother. The painting shown inFigure 4.2 is called the Orologio (the clock tower on the San Marco Square in Venice). Figure 4.3 depicts the

X-ray radiograph of the upper right corner of the painting. In this radiograph the clock plate can be clearlyrecognized, as it was painted using lead white (Pb(CO3)

2.Pb(OH)

2). Additionally, the head of a woman with a


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veil (St. Mary) can be seen holding a nappy in her hands, where a small baby lies. On the right side of the paint-ing, the head of an ox, in the centre of the X-ray radiograph, the head of a donkey with his two long ears, andin the upper right corner, the face of a man with his bald head and a halo (St. Joseph), can be recognized.

Figure 4.2 The easel painting The San Marco Square in Venice with the Orologio (the clock tower) byFrancesco Guardi (1712 1793), oil on canvas, 62.5x 89cm2, Gallery of the Academy of Fine Arts Vienna,

Inv.No. 502.

Figure 4.3 X-ray radiograph of the upper right corner of the painting of F. Guardi, shown in Figure 4.2.

The interpretation of these results by the art historians is that Francesco Guardi used an ecclesiastical paintingof the Nativity and overpainted it with the representation of the Orologio. However, it is rather impossible todraw any conclusion from these results, whether the painting underneath the clock tower of Venice was paint-ed by himself, his father, his brother, or by another painter. Also no information about the materials used in thepainting underneath, as well as in the picture seen by the naked eye, can be gained from such radiographs.

As an example of the application of X-ray radiography to archaeological objects, the results obtained for anEtruscan mirror of the 4th century BC are presented. Figure 4.4 depicts the object with the round metallic mir-ror made of copper, and the handle consisting of two parts. The question of the archaeologists on how thesetwo bones were fixed and held together, can be clearly answered by the X-ray radiographs showed in Figure

4.5, as inside the handle, two thick metallic wires or even parts of a needle (Figure 4.5a) as well as a loop (Fig-ure 4.5b) can be seen.


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X-ray radiography also plays an important role in the field of graphic art, in order to visualize the watermarksof the paper used, for example for copper engravings. In these cases, not the different X-ray absorption of thevarious materials present, but the varying thicknesses of the paper in the area of the watermark are responsiblefor the image.

In Figure 4.6, the copper engravingFides by Johann Christoph Weigel, who lived in the 18th century, is shown.Already in the transmission mode using visible light (Figure 4.7a) the watermark can be made out in the redframed area, but no details can be determined, as the printing ink disturbs the image of the watermark. Forcomparison, the X-ray radiograph (Figure 4.7b) clearly depicts all details of the watermark, as carbon ink,which was used as print material, does absorb soft X-ray radiation similar to the carbon rich paper fibres. Thisfigure thus clearly depicts the watermark: a snake on a shaft or column, based on a coat of arms with themonogram NMH.

Identification of pigments in paint layers by X-ray microanalysis and

micro-XRD

The most common way for studying the stratigraphy of paint layers, as shown in Figure 4.1, has been to takea small specimen containing all layers, to embed the fragment, for example in epoxy resin, and to make a cross-section. The examination of the cross-section by light microscopy, as shown in Figure 4.8, and UV-fluores-cence microscopy, provides sufficient information about the structure of the paint layers, grain size and grainsize distribution of the various pigments as well as varnish layers or organic binding media (Baniketal. 1982).However, for the identification of individual pigments, additional investigations are necessary, where ScanningElectron Microscopy (SEM) in combination with Energy Dispersive X-ray microanalysis (EDX) has been

used widely (Baniketal. 1982; Schreiner and Grasserbauer 1985). In such cases, mainly the backscatteredelectron image with the elemental distribution (X-ray mapping), identifies the most significant elements present

Figure 4.4Front (left) and back side (right) of an Etruscan mirror, 4th century BC,Kunsthistorisches Museum Vienna, Inv.No. VI 3008.

Figure 4.5 X-ray radiographs of the handle of the Etruscan mirror in Figure 4.4.The right image was obtained by tilting the object by 90o compared to the left image.


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Figure 4.6 Fides, copper engraving by J.Ch. Weigel (private property).

Figure 4.7 Image of the object in Figure 4.6 in transmission mode using light in the visible range (left)and X-ray radiograph of the area with the watermark (right) of the engraving by J.Ch. Weigel in Figure 4.6.


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in the pigments and their distributions in the paint layers. Figure 4.9 shows that the first layer consists of Au,which confirms the surface layer to be gold. In layer 2, the main elements are Ca and Pb and/or S. In this case,it is not possible to distinguish between these 2 elements due to the coincidence of S K-lines (2.31keV) withPb M-lines (2.35keV). Ca, as well as S and/or Pb, are also the main constituents of layers 4 and 5.

Figure 4.8 Cross-section of the specimen taken from a mural painting of the Baroque periodwith a thin layer of gold on the surface (layer 1).

Figure 4.9 Backscattered electron image with corresponding X-ray mappings of Au, Ca and Pb.

On the basis of these results, it is mainly possible to surmise the pigments used. However, as many inorganicmaterials, and some of the most interesting pigments, can occur in different crystalline structures, XRD hasbeen proved to be a valuable tool for the clear identification of pigments. With common XRD, it is rather dif-ficult to achieve such results, as the thickness of the paint layers is in the range of several tens microns or evenbelow. Synchrotron X-ray micro-diffraction has been applied recently at the European Synchrotron RadiationFacility (ESRF) in Grenoble/France in order to identify the crystalline structure of the pigments in the cross-section of the paint layers in Figure 4.8. The experimental set-up for micro-diffraction at beam-line ID22 ofESRF, as well as parts of the results, have been published already elsewhere (Hochleitneretal. 2002). In con-clusion, it has to be mentioned that a thin section of approximately 300m had to be prepared from the cross-section in Figure 4.8 prior to analysis, as the micro-diffraction is carried out in transmission mode. As shown

in Figure 4.10a, the complete micro-diffraction analysis was accomplished by the step-wise moving of the thinsection in steps of 4m across the intensive X-ray beam focused by compound refractive X-ray lenses. After


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160 steps, the beam passed through all seven layers of the specimen. Hence, 160 diffraction spectra were ob-tained (Figure 4.10b) representative of the crystalline compounds in the layers, which could be processed andevaluated by Braggs law. This procedure makes the data comparable to tabulated values of known compoundspresent, for example in the collection of the International Centre for Diffraction Data (ICDD). Using the Pow-der Diffraction File (PDF 2000), identification of the crystalline phases, summarized in Table 4.1, could be

achieved.

Figure 4.10 Thin section of specimen in Figure 4.8 for micro-XRD measurements at beam-line ID22,ESRF in Grenoble/France. 160 steps over the thin section (a left image) yielded 160 diffraction patterns

(b right image), which could be evaluated by using the Powder Diffraction File (PDF 2000).

LayerAppearance of the layerin light microscopy

Elements determinedby EDX analysis in theSEM

Phases determined bymicro-XRD

1 yellow Au gold (Au)

2 red/orange Ca, Ba, S and/or Pbbarytes (BaSO

4- permanent

white), calcite (CaCO3

- chalk)

3 transparent C ---

4 yellow C, Ca, S and/or Pbcerussite (2 PbCO

3.Pb(OH)

2- lead

white), gypsum (CaSO4.2H

2O)

5 white Ca, S and/or Pbcerussite (2 PbCO

3.Pb(OH)

2- lead

white), gypsum (CaSO4.2H

2O)

6 white (yellowish) Ca gypsum (CaSO4.2H

2O)

7 white (gray) Ca calcite (CaCO3

- chalk)

Table 4.1 Results of the elemental analysis in the SEM/EDX and -XRD obtainedfor the cross-sectioned paint layers in Figure 4.8.


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XRF and -XRF for the analysis of artefacts

X-Ray Fluorescence analysis (XRF) has been applied widely to material analysis as it is, in principle, applica-ble to all elements except the first two (H, He) of the periodic table. However, many light elements are quitedifficult to measure and require advanced instrumentation, which often limits practical work to atomic num-

bers above 11 (Na). Even in that case, the detection of the characteristic radiation of the elements with anatomic number between 11 and 16 (Na S) is difficult, due to the fact that most of the instruments used fornon-destructive analysis of artefacts have to be air-path systems, and the characteristic radiation of the ele-ments Na S is absorbed by the ambient atmosphere (Mantleretal. 1992; Cesareo etal. 1996; Longoni etal.1998). Additionally, traditional instruments use an X-ray beam of several mm in diameter, which limits theapplication of XRF to specific problems, such as the identification of pigments in miniature paintings or tinydecorations on objects made of glass, ceramics or metals.

The development of micro X-ray tubes, used in combination with poly-capillary lenses for focusing the pri-mary beam to less than 100m, as well as highly sensitive detectors for the secondary X-ray radiation, are anadditional step forward to fulfil the requirements for non-destructive analysis of art objects. In a researchproject2 supported by the European Union, a portable instrument was built, where an X-ray tube by Oxford

Instruments, USA (50kV, 50W), a poly-capillary by X-ray Optics Systems, USA for focusing the primary X-ray radiation, and a silicon drift chamber detector by Rntec, Germany for energy dispersive X-ray analysis,were employed to assemble a compact micro-XRF spectrometer (Bichlmeieretal. 2001). A stage with a smalltable, which supports objects up to approximately 1kg, is further used to move an artefact in three dimensions,in order to select the point to be measured and to adjust the distance between the measuring system and theobject. Additionally, a microscopic unit with a zoom optic enables one to visualize and record the area to beanalysed. The purpose of such an instrument is to permit local, non-destructive analysis in the m-range, andto be transported into museums, libraries and archives in order to carry out the investigations on site.

A scheme of the COPRA2 instrument, and the assembly itself, are presented in Figure 4.11. Figure 4.12 sum-marises the results obtained from a glass fragment of an iridescent Art Nouveau artefact. As the decoration onthe glass surface consists of tiny and fine lines, the micro-beam facility seems to be appropriate. The line scanover such an area depicts the distribution of the elements Pb and Co, as lead oxide has been used to achieve thebright decoration in the blue bulk glass, coloured by additions of cobalt oxide.

Figure 4.11 The COPRA-instrument built within an EU-funded project (note 2).


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Figure 4.12 Fragment of an iridescent glass (top) with the distribution of Pb (bottom left)and Co (bottom right) along the line indicated.

Classification of iridescent glass artefacts of the Art Nouveau by XRF

In a joint research project by the Museum of Applied Arts in Vienna, Austria, the Research Centre Seibersdorf,Austria and the Academy of Fine Arts, in cooperation with the Historical Society in New York, USA, a rec-ognition procedure was developed, which enables a fast and reliable classification of the provenance of ArtNouveau iridescent glass objects (Jembrih-Simbrgeretal. 2000). The procedure is based on non-destructive

Figure 4.13 Art Nouveau glass artifact with iridescent surface of Loetz/Austria.


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analysis using XRF as well as Fourier Transformed Infrared spectrometry (FTIR). The data obtained are proc-essed and statistically evaluated in a self-written software package based on multivariate (cluster) analysis.Furthermore, a characterisation of the manufacturing technology of the thin iridescent surface layer has to becarried out in the project in order to obtain the differences as well as the similarities between the two mostimportant Art Nouveau glass companies, Tiffany in the USA and Loetz in Austria (Figure 4.13).

Iridescence itself is an interference effect, occurring whenever bulk material is coated with a very thin layer,with optical properties different from those of the bulk. Therefore, XRF measurements were carried out duringthe project on the iridescent and the non-iridescent sides. Fragments of Tiffany and Loetz glass, as well as halfproducts available in the Museum of Applied Arts in Vienna and the New York Historical Society, could beinvestigated. For comparison, also fragments of Aurene Glass, USA and glass by modern artists and manufac-turers such as Jack Ink, Austria and Strini Art Glass, California, were included. The intensities of the variouselements determined by XRF were used as an input for the statistical pattern recognition. As can be seen inFigure 4.14, the results of the factor analysis show a clear differentiation between Tiffany and Loetz. Addition-ally, the products of Aurene, Jack Ink and Strini Art Glass, form clusters also due to the chemical compositionof the bulk glass as well as the elements present in the iridescent surface layer.

Figure 4.14Results of the factor analysis considering the elements Si, K, Zn, and Se in the bulk glass and Pband Ag in the bulk and the iridescent surface layer (Jembrih-Simbrger 2000).

Conclusion

X-ray radiation has been useful and used for characterising artefacts since it was investigated in 1895 by W.C.Rntgen. The method of X-ray radiography provides insights into an object, its structure and in some caseseven the identification of the manufacturing process. As this technique is in a strict sense non-destructive, it

accords well with the way an art historian, archaeologist or a conservator would look at works of art, and there-fore found early wide acceptance.


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Methods based on X-ray analysis such as X-ray fluorescence or X-ray diffraction analyses are more complex.However, as the booming development in electronics and computer technology brought us new analytical in-struments of great perfection, such techniques are also widely used for the material characterisation of an arte-fact. With portable XRF-instruments, the determination of the chemical composition can be carried out di-rectly in a museum or at an archaeological site; on the other hand, XRD with synchrotron radiation enables the

complete structural analysis of samples in the micro-dimension or even in the nano-range.

Nevertheless, it should be mentioned that the quality of the results depends to a large extent on the posing ofthe sensible question in context with the artefact. The conservation scientist finds himself in a difficult position,as he has to interpret this question by a conservator or pure scientist and deal with an abundant stream of data.These data almost never speak for themselves; they need careful interpretation and comparison with other re-sults.

Acknowledgements

The authors want to express their sincere thanks for the co-operation and intense discussion of the objectives

as well as of the results obtained by various analytical investigations: Dr. M. Fleischer, curator at the Galleryof the Academy of Fine Arts, Mag. Zhuber-Okrok, curator of the Kunst-historisches Museum Vienna, and Prof.Mag. H. Holle, paper conservator at the Conservation Department of the Academy of Fine Arts.

Endnotes

1 Parts of this contribution were already published in Powder Diffraction 19/1 (2004) 3-11.

2 COPRA (A compact Rntgen analyzer), Project No. STM4 CT 98 2237, 4 th Framework Programmeof the European Union, DG XII.

References

Baer, N.S. and Low, M.J.D. 1982. Advances in scientific instrumentation for conservation an overview. InScience and technology in the service of conservation. Reprints of the IIC-Congress Washington/DC, Sept.3 9, 1 - 4.

Banik, G., Schreiner, M., Stachelberger, H. etal. 1982.Praktische Metallographie 19: 104 - 108.

Bichlmeier, St, Janssens, K., Heckl, J. etal. 2001X-Ray Spectrometry 30: 8 - 14.

Cesareo, R., Gigante, G.E., Canegallo, P. etal. 1996NIM-A 380: 440 - 445.

Hochleitner, B., Schreiner, M., Drakopoulos, M. etal. 2002 Non-destructive testing and microanalysis for thediagnostics and conservation of the cultural and environmental heritage. In proceedings of Art 2002, Ant-werp June 2 - 6.

Jacobi, R. 1941Angewandte Chemie 54: 28 - 29.

Jembrih-Simbrger, D., Neelmeijer, Ch., Schreineretal. 2000.Microchim. Acta 133: 151 - 157.

Jerem, E. and Biro, K.T. 2002.Archaeometry 98. In proceedings of the 31st Symposium. BAR InternationalSeries 1043, London.

Kuehn, H. 1993. Lead-Tin Yellow. InArtists Pigment, Roy, A. (ed.), Oxford University Press, New York Oxford, 2: 83-112.


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Lang, J. and Middleton, A. 1997.Radiography of cultural material. Butterworth - Heinemann, Oxford.

Longoni, A., Fiorini, C., Leutenegger, P. etal. 1998NIM-A 409: 407 - 409.

Mairinger, F. and Schreiner, M. 1982. New methods of chemical analysis a tool for the conservator. In Sci-

ence and technology in the service of conservation. Reprints of the IIC-Congress Washington/DC, Sept. 3 9, 5 - 15.

Mairinger, F. 2003. Strahlenuntersuchung an Kunstwerken. E.A. Seemann Verlag, Leipzig.

Mantler, M., Schreiner, M., Weber, F. etal. 1992.Advances in X-ray Analysis, 35: 987 - 993 and 1157 - 1163.

Mantler, M., Schreiner, M. and Schweizer, F. 2000. Museum - Art and Archaeology. InIndustrial applica-tion of X-ray diffraction. Chung, F.H. and Smith, D.K. (eds.) Marcel Dekker, New York - Basel 621 - 658.

Schreiner, M. and Grasserbauer, M. 1985.Fres.Z.Anal.Chem. 322: 181 - 193.

Schreiner, M., Linke, R. and Jembrih, D. 2000. Non-destructive analysis of artefacts by XRF present state,trends and perspectives. In:Art et Chimie, J. Goupy, J. and Mohen, J.P. (eds) CNRS Editions, Paris 169 -175.

Vandiver, P.B., Druzik, J.R., G.S., Wheeler, G.S. etal. 1992.Materials issues in art and archaeology III. InMaterials Research Society Symposium Proceedings, 267, Pittsburgh.

Van Grieken, R., Janssens, K., Vant dack, L. etal. 2002.Non-destructive testing and microanalysis for thediagnostics and conservation of the cultural and environmental heritage. In proceedings of Art 2002, Ant-werp June 2 - 6.

Authors address

Manfred Schreiner*, Bernadette Frhmann and Dubravka Jembrih-Simbrger, Institute of Science and Tech-nology in Art, Academy of Fine Arts, Schillerplatz 3, A-1010 Vienna, Austria.

* Correspondence should be addressed to Manfred Schreiner ([email protected]).


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5 Material analysis in architectural paint research

and restoration of wall paintings

Mads Christian Christensen

Abstract Analysis of cross-sections from micro-samples taken from architectural decorations is a versatile method to gather informa-

tion about the composition of paint layers. In order to gather the greatest amount of information from micro-samples, a combination ofanalytical techniques must be used. Optical microscopy combined with Low-Vacuum Scanning Electron Microscopy with EnergyDispersive Spectroscopy (LV-SEM-EDS) and vibrational spectroscopy such as Fourier Transform Infrared Spectroscopy (FTIR) andmicro-Raman spectroscopy are versatile tools for the characterisation of pigments and fillers in cross-sections from architectural deco-rations. Media analysis with Gas Chromatography Mass Spectrometry (GC-MS) can supplement the information gained from thecross-sections.

Analysis in relation to conservation of wall paintings deals with the identification of pigments, binding media and their degradationproducts, analysis of the composition of mortar and plaster as well as characterisation of salt efflorescence. At the National Museum ofDenmark, micro samples from wall paintings are normally analysed by various techniques including SEM-EDS, FTIR and micro-chemical tests.

Keywords Architectural paint; wall painting; cross-sections; low-vacuum scanning electron microscopy energy-dispersive spectros-copy; vibrational spectroscopy

Introduction

Architectural paint research involves the analysis of layers of accumulated paint on a decorated surface. It isan important technique for establishing colours of historic paint, and reconstructing a room or a facade froman earlier time. Architectural paint analysis is often performed when secular historical buildings are restored,and when colour schemes of past periods in the building are elucidated. The original colour schemes are oftenreconstructed during the restoration process.

In Northern Europe, wall paintings are found in many of the medieval churches. Often the paintings have beencovered with layers of lime-wash. The goal of the scientific examination in such cases, is to gather sufficientinformation about the paintings, that one can understand the iconography of the motifs and choose an appropri-

ate restoration process that can preserve the original wall painting in situ. In the early 20th

century, the paintingswere often detached and brought to museums. This practice is very rare today where the paintings are kept intheir original context in the church and on their original support (Brajer 2002).

Analysis related to architectural paint research

Information on the identity of the components of paint layers can be used both to reconstruct certain types ofpaint and also to date the paint layers. Detailed understanding of the building structure, which is obtained dur-ing the analytical process, is often used to establish a decorative scheme similar to the original.

The simplest method of paint examination is to uncover the earlier paint layers by removing them succes-

sively. This can be done mechanically or chemically, by scraping with a scalpel blade or by applying solventsto the paint layers. This method is fairly destructive, but the skilled conservator can rapidly reveal a stepped


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sequence of layers of paint. A more advanced method of analysing the layered structure is to prepare embeddedcross-sections and analyse the paint layers by microscope. Sampling of cross-sections can be done by micro-destructive methods, which are almost invisible to the naked eye (Figure 5.1). Embedding of cross-sections isnormally done with epoxy or polyester resin. The samples are polished with silicon carbide paper after whichsamples are examined by optical microscopy.

Figure 5.1 Sampling cross-sections with a device constructed by restoration architect S. Lundquist.

The number and the thickness of paint layers are determined, and the types of pigment and binder are tenta-tively characterised on the basis of features such as transparency, grain morphology, and relative refractiveindex. UV- fluorescence microscopy can be used to characterise transparent layers such as varnishes. Phot-omicrography and sketching are important tools in interpreting and documenting the layered structure found incross-sections. Microchemical tests can also be performed directly on sections and, in this way, materials likelead white or starch can easily be characterised. If one wants further information from the sections, it is neces-sary to use instrumental methods. Combining optical microscopy, Low Vacuum Scanning Electron Microscopy

with Energy Dispersive Spectroscopy, (LV-SEM-EDS) and vibrational spectroscopic methods on cross-sec-tions from architectural decorations are powerful methods.


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Low vacuum scanning electron microscopy with energy dispersive spectroscopy

Conventional scanning electron microscopy with energy dispersive x-ray spectrometry (SEM-EDS) is a versa-tile tool for mapping elements in layered structures. The method, which requires prior sputtering of the samplewith carbon or gold in order to allow it to conduct electrons, has been used for examination of cross-sections

from pictorial art. By contrast, the advantage of the LV-SEM-EDS- system is that it is a non-destructive tech-nique because no such preparation of the sample is needed before the analysis. The analytical system allowsfor the detection of all elements heavier than boron, and the software allows one to carry out line scans andpoint analyses. A speed map facility makes it possible to survey a sample and establish the distribution ofconstituent elements in the samples (Link 1995).

Vibrational spectroscopy

FTIR microscopy has been applied to molecular mapping studies on cross-sections from pictorial art (Derricket al. 1999). Van der Weerd used a FTIR imaging system, a focal plane array and a step scan interferometer inhis investigation of cross-sections from traditional oil-paintings (Van der Werd 2002). Kendix et al. demon-strate

Documents

16402120 COST G8 Benefits of NonDestructive Analytical Techniques for Conservation