methods and techniques to retrieve ancient ...

METHODS AND TECHNIQUES TO RETRIEVE ANCIENT POLYCHROMY. AN OVERVIEW M.J. Merchán1, P. Merchán2 1

Universidad Pablo de Olavide (SPAIN) Universidad de Extremadura (SPAIN) [email protected], [email protected] 2

Abstract In this paper we try to summarize and give an overview of archeometric methods, both chemical analysis and physical tests, which have been used for the recovery of the colour in ancient sculpture until today in such a way that, considered diachronically, we can assess the results obtained by those that have more predicament today. From the vision provided by this cast of techniques and results, we will be able to outline a working hypothesis that address future research needs in this field. In addition, to be capable of incorporating the technology necessary for obtaining colour remains to others as the 3D digitization can guess an unavoidable task. This would allow that, with one mere campaign could be performed two tests essential to the complete understanding of the material by an archaeologist today, avoiding excessive manipulation of sculptural or architectural remains. Keywords: Archaeology, polychromy, sculpture, technology.

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INTRODUCTION

We would like to introduce you in this theme joining the reasons given by P. Liverani [1] about the importance of retrieving polychromy of ancient work of arts. He pointed out that colour was not an accessory but a constitutive element of them, not only from a perceptual point of view but also from a semantic one, since a series of important messages and connotations were assigned to this medium of colour. Such is the case that the absence of colour or its lack of consideration can lead us even to a misunderstanding of works of art and of ancient artistic culture. He remarks as a second reason, once we are already in our field of investigation, the fact that the colour can be considered as the fourth dimension of sculpture that imposes itself and determines the three spatial ones. Its relevance is proved since the sculptor could modify and revise this dimension more freely than other plastic forms in order to adapt the work of art to the taste of the period, to the demands of the patron and to its function. Archaeologist and researchers agree with these ideas realize that it’s necessary a new revision of the more frequently tested interpretation schemes concerning the relation between originals and copies and for the total comprehension of this phenomenon. Finally, Professor Liverani asserts the importance of these themes from the point of view of protection and conservation of works of art and the urgency of creating the sensibility among specialists considering that unrecognized traces of colour can easily be damaged or removed by rushed operations of excavation, restorations and conservation. Because if we don’t get it,if in these years we are not be able to develop an appropriate sensibility, we could be moving towards irreparable damage. Having said which it’s revealed evident that any good intention in this sense, any novel movement that wants to be developed in this direction, born in ballast if it arises in a monolithic and unidirectional manner. Without the contribution of tools that provide the eminently scientific disciplines would be impossible to get the desired results. This fact is markedly stated in an area such as the archaeological research in which, since several decades ago, a new line of study that tries to retrieve the polychromy in ancient statuary and architecture has appeared or, to put in another way, as we’ll see infra, is being updating. Although the researchers engaged in this new branch are aware of using and developing the new technologies, they considered that they already are “at the beginning of the beginning”. [2]

Proceedings of INTED2013 Conference 4th-6th March 2013, Valencia, Spain

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ISBN: 978-84-616-2661-8

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RETRIEVING COLOUR IN CLASSICAL SCULPTURE. AN HISTORICAL SUMMARY

In the classical sources we can find several data concerning to sculptors, sculptures and ways of work both in marble and in bronze. Through the information that has come to us from them it might be supposed that the final image that the spectator saw of the ancient sculpture was that of a totally polychromatic representation. But in spite of the fact that the ancient authors worried about trying to transmitted to us such a thing, during many phases of the history of the archaeological investigation, in his few ones of 200 years of existence, there was ignored, consciously or not, that this was like that, as we will see in the following lines.

2.1

At the beginning: Renaissance

Though the recovery of the Laocoonte marked the beginning of the new and most important artistic and cultural current, the Renaissance, overcoming thus the medieval mentality dragged for centuries, in the case that occupies us, it contributed to the bad interpretation of the classic sculpture. The principal contribution to this fact was that the statuary used to appeared in the whole whiteness of the marble in which it was made, without remains of the polychromy that we can affirm today it would have. The finding of other relevant Roman sculptures without remains of color led the men of the epoch to thinking that the artistic Greek and Roman past had been as it had come to them, in the natural color of the marble in which the pieces were done. Geniuses like those of Michelangelo or Leonardo took charge that such a conception was spreading as well as the Accademia, founded by Il Vasari, in Firenze.The school’s doctrines were based on certain principles like the demand for an idealizing mode of depiction in emulation of prominent Antique sculptures in white marbles, as they would have been in view of the recovered vestiges. That was the authoritative model until well into the nineteenh century. Here we are, as Ostergaard defends, at the cradle of the black-and-white perspective of the scholarly investigation of European sculpture, and its aestahetic blindness to polychromy [3].

2.2

Born of Archaeology

The Neoclassicismus, as his own name indicates, furthermore supposes the idealization of the classic past, Greek and Roman, as a role model always inside the monochromy they supposes to its sculptural and architectural creations. Men of this time consider that the polychromatic statues was something found in country churches and admired by peasants. Nevertheless it is also in this epoch, concretely in 1763, when Johann Joachim Winckelmann published the first edition of his groundbreaking work known in English as The History of the Art of Antiquitiy [3], starting point of a new methodology of historical investigation that will suppose the birth of the Archaeology as scientific discipline. A scholar like Winckelmann could not ignore the new findings that were taking place in which the remains of the original colour were evident and in this way he reflected it in his book. However, he is not normally credited with the discovery of the polychromy of ancient greek marble sculpture. Quite to the contrary, the editors of the so-called “Wiemer edition of Winckelmann’s works”, several decades after his first publication, felt the need to set back the date of the polychrome sculpture mentioned by this author in order to preserve the vision of a classical period of white marble classical statuary since they were deeply influenced by Herde’s intransigent verdict against polychromy in general [4]. That’s why in the future all archaeologist will think that the opinion of Winckelmann about classical statuary was “the whiter, the better” [3]

2.3

XIX Century up to the Second World War

In the 19th century, while the most academic current continued with the traditional vision of a monochrome sculpture, the trips of adventurers and investigators to visiting in situ the Greek places became increasingly numerous, imbued of the spirit of the Romanticism and the desire to free Greece, the mother land of the democracy, of the Ottoman domination. This led to new expeditions and excavations to the Greek site in order to rediscover cities, temples and shrines, hitherto known only by the classical sources. The remains that were appearing spoke in an undoubted way of that the Greek antiquity had been in colours. Archaeological discoveries of the second half of the century then, that took place not only in Greece but even in Rome itself, shifted the weight in favour of colour in classical time. By the end of the century, all but the most stubborn defenders of white faith had admitted that colour was an integral element of Antique sculpture and architecture. However, it still had not raised the study and the

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systematization of polychrome classical statuary from a scientific point of view since hitherto it was more like an art-historical and, even, aesthetics question. It will not be up to the beginnings of the 20th century when W. Lermann carries out for the first time scientific studies on the pigments that remains in the Athenian korai, developing the pioneering studies made by Faraday, but the work he carried out then can be considered as an unicum [5]. Once entered in this century, the new cultural, ideological and political movements as well as the warlike periods that devastate Europe made that they forget this conception of the classic archaeology and return to the traditional monochromatic vision.

2.4

Back to the starting point. A new beginning

Thanks to the labour of compilation carried out for P. Reuterswärd [6] the studies on polychromy lived a new beginning since Humanity had already forgotten everything what had been discovered in the last century about this point. From early 1960s onwards is the German school the one that awards a new impulse to this line of investigation taking advantage of the possibilities that the news in the technology of its time could offer to the researchers. Thus, starting with a simple method developed by themselves, the photographing of the objects illuminated from different angles, the so-called ranking light, they could recovery, from which scrappy guides made in the marble’s surface, the brands and lines utilized by the painters so to be guided when they had to apply the colour and to do his compositions. But also more sophisticated technologies were in use in order to retrieve remains of colour as infrared and ultraviolet photography that contributed substantially to the development and knowledge of this new line of research [3]. From the last 20 years of last century to the present day the interdisciplinary cooperation between the different scientific branches involved in this process has been fundamental for the development of it. They were involved: classical archaeology, classical philology, Chemistry, Physics, Engineering and Conservation and Natural Sciences. A factor of equal importance was the increased employment of refined methods of technical photography as well as analytical high technology developed by other disciplines different from archaeological one [3]. Among them it is used in situ microscopy, photo-induced luminescence imaging (VIL/UIL), Raman spectroscopy, scanning electron microscopy (SEM); Fourier transform infrared spectroscopy (FTIR), performed on an equipment with Continuum IR microscope and often supplied with MCT/A detectors; high performance liquid chromatography (HPLC), gaschromatography-mass spectrometry (GC-MS) as well as minero-petrographic and isotopic analyses [7].

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TRACKING COLOUR IN CLASSICAL SCULPTURE NOWADAYS

What kind of these technologies should be used in each case or if we will choose between noninvasive techniques or invasive analytical methods is frequently determined by the material to be studied itself. We also we have to take into account the working environment, the permissions to take samples we can obtain and above all the type of research project we are carrying out and its objectives [7] [8]. One preliminary visual examination on the sculptural surfaces would be very helpful in order to choice the methods to employee. If we complement this primary inspection with the use of stereo microscope with a magnification range, that don’t have to be too large to be effective, we will be allowed to clarify initial questions and develop further aims of investigation as well as to select the most suitable technology [8]. The perceptual capacity of the human eye can be supplement substantially by photographic techniques
since they can provide spatial information on the distribution of different materials.
Photoinduced luminescence photography or imaging, records the steady-state emission from a chemical compound continuously excited by electromagnetic radiation. Photography under ultraviolet (UV)induced luminescence imaging in the visible (VIS) range is the most commonly exploited technique for the examination and characterization of painting materials such as organic binders and varnishes. UV fluorescence -with a camera which should be equipped with a strong UV blocking filter- intensifies the contrast and marginal sharpness of the polychromy that comes into view. The reflection of UV radiation is invisible to the human eye, but not to the camera. For a UV reflectograph, a black glass filter should be mounted in front of the lens [8] [9].

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Although much less common than UV-induced luminescence, VIS-induced luminescence imaging is a non-invasive investigative technique that can help in the characterisation of painted surfaces. In this case, the excitation wavelength(s) lies in the visible range and is governed by the types of radiation sources used. A few inorganic pigments, among which are Egyptian blue, Han blue, Han purple, cadmium red and cadmium yellow, show strong photo-induced luminescence properties, with emissions in the IR when excited in the visible range [9]. Regarding to the invasive techniques, the first thing we want to point down is that the removal of samples for this purpose represents an unwanted intervention into the original piece. Upon removal, the sample loses its relationship to the local context. Layer sequences provide information, but frequently it is difficult to separate the individual layers or assign them to the sequence of the reconstructed application of paint. Reliable analysis results can be obtained with FTIR spectroscopy, performed on an equipment with Continuum IR microscope; XRF analysis and energy-dispersive Xray spectroscopy on a scanning electron microscope (EDX analysis) as well as simply by viewing through a scanning electron microscope. When Raman Spectroscopy is used this test is carried out with a spectrometer using green and near IR laser, a liquid nitrogen cooled CCD detector and a microscope system. If we want to use HPLC technique have to be extracted a sample of a few micrograms that have to be several of them in a GC-MS test because each sample are hidrolyzed, dried again and then almost burned at 300º in order to get the mass spectral data to interpret. Thank to this technology it was able to found complex mixtures of pigments and selected pigments for specific areas, the ones that were used to create subtle tonal variations in ancient sculptures and reliefs where these tests were done. These included: calcite, red and yellow ochres, carbon black and Egyptian blue for the flesh tones; calcite to provide highlights on the flesh areas; lead white and Egyptian blue for the eyeballs; a red organic colourant in the nostrils, the lachrymal ducts and the inner parts of the mouth; and red and yellow ochre for the hair. [7] [8] [9].

3.1

Some examples

The most active groups in this respect are those that work in the Ny Calrsberg Glytothek, to Jan Stubbe Ostergaard's order, and in the Brithish Museum, led by Giovanni Verri. Both groups, probably for belonging to very powerful institutions, have a major accessibility to a series of means to work in this sense and to a major both technical and economic capacity that has allowed them to carry out the most top studies till now known together with those performed by Brinkmann. These studies have provided spectacular results and have become an elemental reference to the researches that wants to approximate to this renewed discipline. Of those works are the samples that follow.

Fig. 1: VIL-image of the left foot. On the flat surface of the instep a clearly defined band of Egyptian blue is observed glowing bright white, whereas in the incisions of the ankle strap the Egyptian blue appears as small shining grains like beads of a necklace. In [11], p. 41, Fig. 16

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The marble slab presented as Fig. 3 was removed by Sir Stratford Canning in 1846 from the castle of St Peter, where it had been reused as a decorative building material. Thanks to the VIL image of the detail named as Fig. 3b we can see how surviving particles of Egyptian blue are shown in the shape of a sword in the proper right hand of a Greek warrior and how some remains of colour could be detected in the folds of the drapery of an Amazon. It has long been known that the male Greek warrior held a painted sword in his clenched right fist as it can be dimly made out with the naked eye. However, the VIL image clearly shows the shape, indicated by the surviving Egyptian blue. It is thought that the sword was not originally intended to be painted in blue but instead it was gilded or silvered over an Egyptian blue background. For the Amazon figure, while traces of red pigment can be seen on the mantle with the naked eye, no visible traces of blue survive. However, the VIL image reveals the presence of particles of Egyptian blue within the deepest recesses of the folds.

Fig. 1 Visible (a) and VIL (b) images of a detail of the Amazon frieze from the Mausoleum at Halikarnassos (c. 350 B.C., BM 1847,0424.4). In [10], p. 222, Fig. 5.

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4 4.1

PRESENT AND FUTURE Current reality

Though the panorama that we present in the previous lines seems to be encouraging enough there are many problems facing researchers who have decided to pursue this new line of knowledge. Firstly, the shortage of means does that each one uses the most accessible methods to his needs. This entails that doesn’t exist an established protocol, an homogeneity in the used of techniques and technologies that makes that the results obtained by different teams could not be comparable. There is also added the handicap of being groups widely dispersed so the sharing of results, access to data from other research, the compilation of all of them to develop reference tables to serve as a starting point for anyone who want to do their own research turn into impossible. In this respect a new initiative has arisen in the Ny Carlsberg Glyptothek that tries to assemble all the results in a great database accessible to the whole world where the scanty results till now obtained can be centralized.
 They would like to create a platform for the project, where scholars would be able to share data and the public would be given access to the research. This first online database exclusively for research on ancient sculptural polychromy pretends to be a research storage and communication platform, a bibliographical database and a database of the sculptures known to have traces of colour. At present days they continue working in this respect though the lack of contributions on the part of other institutions undoubtedly will limit the usefulness of this useful tool [12]. In addition, those involved to recover the colours of ancient statuary still have to face the incomprehension of a great majority of specialists, stuck to the ancient monochrome vision, who largely still ignore them as best. But the biggest problem takes root in that the repertoires of images that are used in the formation of new historians of art or archaeologists continue presenting the statues in the condition in which are preserved today, in white marble mostly. Due to his fact, students have no direct experience with the color palette and the actual appearance of the sculptures that are being studied. Similarly, the general public visiting museums and sites face the pristine remains of a glorious past that now is shown in the nudity of the marmoreal surface. The mere mention of the polychromatic reality doesn’t turn out to be sufficient to change a mentality educated in a few rules for decades.

4.2

Future goals

From the vision provided by this cast of techniques and results, we are able to outline a working hypothesis that address future research needs in this field. From what we've seen so far it has been demonstrated as essential being capable of coordinating the diverse groups that till now are dealing with these topic and that work in an isolated way. It would also be very important the implication of the countries that formed the Roman Empire. This is essential in order to get a better view of the polychrome phenomenon in antiquity and the various techniques used to carry out. These teams certainly have to be multidisciplinary and include specialists of all the matters involved in this process. An essential goal in order that the investigation continues growing would be the creation of a protocol of common work, in order that all the tests were done in a homogeneous way, independently of the team that performed them in order that the results could be compared. The project of creating a large database that contained all the data obtained thus seems imperative to centralize knowledge, whether on one platform or on different platforms interconnected to make information accessible to everyone who wants to consult them. It would also be required increased awareness on the part of the institutions since the material for these investigations is not economically affordable for a lot of groups now formed. Without a doubt whatsoever, in the future technological development will permit to increase investigation strategies and simplify several of the methods used nowadays, too heavy and expensive to be used easily. For example, the measurement device industry is already now announcing the production of a new generation of robust, easy-to-handle devices which can be used efficiently regardless of the temperature [8]. In addition, to be capable of incorporating the technology necessary for obtaining colour remains to others as the 3D digitization can guess an unavoidable task. This would allow that, with one mere campaign could be performed two tests essential to the complete understanding of the material by an archaeologist today, avoiding excessive manipulation of sculptural or architectural remains. In this respect some projects are already carried out as the one that arises from the recovery of an Amazon's head in Herculano [13]. However, this is done by first creating a three dimensional model and in a subsequent process, adding the color data. Future goals would be that of being capable of obtaining

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both data sets in a single process, implementing the technologies hitherto known or developing new others that achieve these objectives. Having all this information would allow us to be closer than ever to the sculptures as his creators conceived them. Finally, the ultimate goal of this paper is to draw a few guidelines to follow in developing educational programs of all disciplines covering this line of research so that university students interested in training it can acquire the tools and skills enough with which to develop their knowledge in the field of research. To obtain this aim is necessary the total involvement of the universities both at the institutional level and in the part that concern to the professorship. Starting with the teaching process of the classic archaeology at the varying degrees in which this discipline is imparted, we consider very helpful introduce a photographic extended catalogue that includes all material provided by research on polychromy. This simple action will allow star forming the consciences in this sense of future specialists. It is also necessary to begin to introduce eminently scientific matters between the humanistic subjects since the current world requires the formation of the modern archeologist in disciplines traditionally far for their training camp. The specialization of the students in this renewed line of research, through formative courses or masters, would be one of the most important tasks to get to ensure its continuity and the possibility of a larger growth in the most near future.

REFERENCES [1]

Liverani, P. (2009). The Polychromy on Stone in Roman Imperial Times: an overview. Proceedings of the Second International Symposium of Conservation and Research of the Terracotta Army and Polychrome Cultural Relics (Xian 23-25 March 2009), pp. 387-395.

[2]

Ostergaard, J.S. (2010). The Sciarra Amazon Investigation: Some Archaeological Comments. Tracking Colour. The polychromy of Greek and Roman sculpture in the Ny Carlsberg Glyptotek. Preliminary Report 2, pp. 50-60.

[3]

Ostergaard, J.S. (2010). The Polychromy of Antique Sculpture: A Challenge to Werstern Ideals? Circumlito .The polychromy of antique and mediaeval sculpture, pp. 78-105.

[4]

Primavesi, O. (2010). Artemis, Her Shrine and Her Smile: Winckelmann’s Discovery of Ancient Greek Polychromy. CircumlitioThe polychromy of antique and mediaeval sculpture, pp. 24-77.

[5]

Brinkmann, V. (2004). I colori del bianco. Policromia nella scultura antica.

[6]

Reuterswärd, P. (1960). Studien zur Polychromie der Plastik: Griechenland und Rom. Untersuchungen über die Farbwirkung der Marmor- und Bronzeskulpturen.

[7]

Verri, G.; Opper, T. & Deviese, T. (2010). The ‘Treu Head’: a case study in Roman sculptural polychromy. The British Museum Technical Research Bulletin 4, pp. 39-54.

[8]

Brinkmann, V. (2010). Statues in Colour: Aesthetics, Research and Perspectives. Circumlitio. The polychromy of antique and mediaeval sculpture, pp.10-21.

[9]

Verri, G. (2009). The spatially resolved characterisation of Egyptian blue, Han blue and Han purple by photo-induced luminescence digital imaging.
Anal Bioanal Chem DOI 10.1007.

[10]

Verri, G. and Saunders, D. and Ambers, J. and Sweek, T. (2009). Digital Mapping of Egyptian Blue: Conservation Implications. Rozeik, C and Roy, A and Saunders, D, (eds.) IIC. The International Institute for Conservation of Historic and Artistic Works, pp. 220 - 224.

[11]

Sargent, M.L. and Therkildsen, R.H. (2010). Research on Ancient Sculptural Polychromy with Focus on a 2nd Century CE Marble Amazon. Tracking Colour. The polychromy of Greek and Roman sculpture in the Ny Carlsberg Glyptotek. Preliminary Report 2, pp. 27-49.

[12]

Skovmøller, A. Tracking Colour Online: Managing and Sharing the Digital Assets of the NCG/CPN Project. Tracking Colour. The polychromy of Greek and Roman sculpture in the Ny Carlsberg Glyptotek. Preliminary Report 2, pp. 61-68.

[13]

Earl, G.; Beale, G.;Happa, J.; Williams, M.; Turley, G.; Martinez, K. and Chalmers, A. (2009). A re-painted Amazon. EVA 2009 London Conference.

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