British Museum Technical Research Bulletin

Technical Research Bulletin Volume 3

Volume 4

The publication of this fourth volume of the British Museum Technical Research Bulletin coincided with the broadcast of the series A History of the World in 100 Objects, a joint project between the British Museum and BBC Radio 4. Technical examination and analysis were undertaken on many of the objects that featured in the radio series. The results allowed a deeper understanding of the creation, function and subsequent history of these artefacts, which contributed to the development of programme scripts.

A particular theme that recurred throughout A History of the World in 100 Objects was the transmission of ideas and materials within and between cultures, through trade, exploration or incursion. Four articles in this volume explore the evidence for such cross-cultural diffusion, ranging from the Greeks trading in the port of Naukratis in sixth century BC Egypt to the convergence of Ethiopian and European iconography and pigments in a mid-nineteenth century Ethiopian painting of the crucifixion.

Popular views of conservation and scientific examination often focus on questions of attribution or authenticity, and studies that lead to the exposure of a fake or pastiche make good stories. Two papers in this volume address questions of authenticity: examination clearly shows that swords attributed to the late second and first millennium BC from modern day Iran are not what they purport to be; while analysis of a polychrome Roman marble head from the mid-second century AD (the Treu head) has re-established it as a rare survival of original Classical polychromy.

All articles have been anonymously peer-reviewed by specialists outside the British Museum.

Articles

The image revealed: study and conservation of a mid-nineteenth century Ethiopian church painting
Heidi Cutts, Lynne Harrison, Catherine Higgitt and Pippa Cruickshank

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Summary
An Ethiopian mural painting on a cotton support, The Crucifixion of Christ (Af1893,1112.1), was donated to the British Museum in 1893. The preparations for its exhibition brought together a multi-disciplinary team of British museum professionals and community advisors from both the UK and Ethiopia to fully research, analyse and conserve the painting, which is thought to be unique both in scale and subject matter. Translation of the Ge’ez inscriptions revealed the complex interplay of secular and religious narrative for the first time. Depicting the Crucifixion and scenes from the passion, the painting also shows key episodes from the life of Bishop Selama, head of the Ethiopian church until 1867. The scene showing the coronation of Emperor Tewodros II dates the painting to after 1855.

The painting materials and techniques were characterized and showed that a range of imported pigments was employed. It also showed that the apparent absence of a yellow pigment, which suggested that the painting might be unfinished, is caused by the degradation of the yellow pigment orpiment. This allowed the painting to be understood as a finished work, albeit one much altered in appearance and condition. The early inclusion of synthetic ultramarine, a bright blue pigment, in the palette is of note.

The fragile condition of the painting, which resulted from a combination of the materials, technique, construction and previous storage conditions, necessitated treatment. Drawing on both textiles and paintings conservation disciplines, the conservation strategy that was adopted has stabilized the painting. It is now mounted on a solid padded board and is more appropriately displayed, revealing the work in its entirety and allowing greatly improved access to this unique object.

 

Coatings and contents: Investigations of residues on four fragmentary sixth century BC vessels from Naukratis (Egypt)
Rebecca Stacey, Caroline Cartwright, Satoko Tanimoto and Alexandra Villing

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Summary
The use of organic coatings on unglazed ceramic vessels, to seal surfaces and decrease permeability, has a long history extending from prehistory to modern traditional potters. A range of substances has been used, often water-insoluble natural products that tend to survive well under archaeological conditions. Identification of these coatings provides useful insights into past vessel production and properties and may also offer opportunities for interpretation of re-use and circulation of vessels. Results are presented here from the investigation of coatings on a small number of sixth century BC vessel sherds from Naukratis (Egypt). All the deposits were found to be composed of pitch derived from conifer wood, which may be the remains of linings used to seal the vessels or residues of the vessels’ contents. In one case, fig pulp and ‘seeds’ are associated with the pitch, which seem not only to suggest that the pitch was used as a lining, but have also offered a rare opportunity to elucidate both the sealing technology and vessel contents. The results are considered in terms of the broader interpretation of the past use of organic coated vessels and highlight the benefit of a multidisciplinary approach to organic residue analysis.

 

A gold four-horse model chariot from the Oxus Treasure: a fine illustration of Achaemenid goldwork
Aude Mongiatti, Nigel Meeks and St John Simpson

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Summary
This paper outlines the results of the first scientific study of a delicate gold model of a four-horse chariot complete with driver and passenger, found in a large hoard of gold and silver artefacts known as the Oxus Treasure. This treasure is one of the most important surviving assemblages of sumptuary metalwork from the period of the Achaemenid Empire. It consists of about 180 objects, dating mainly from the fifth and fourth centuries BC, plus a large number of coins. The present technological study builds on previous analyses of Achaemenid silver and gold pieces in the British Museum collection. Microscopic examination, X-radiography and scanning electron microscopy combined with energy dispersive X-ray analysis have revealed undocumented evidence for the skill of the Persian goldsmith in creating an intricate artefact produced from a variety of techniques, such as repoussé and chasing on gold sheets, granulation, wire twisting and hammering.

 

The ‘Treu Head’: a case study in Roman sculptural polychromy
Giovanni Verri, Thorsten Opper and Thibaut Deviese

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Summary
This contribution presents recent work on an important Roman marble head of the mid-second century AD from the collection of the British Museum (1884,0617.1). The head was found on the Esquiline Hill in Rome in 1884 and soon after its discovery was acquired for the British Museum. Unusually, it retained extensive traces of its original polychromy, including otherwise rarely preserved skin pigments. Ever since the German scholar Georg Treu published the sculpture in 1889, it has played a significant part in the discussion of ancient sculptural polychromy and in particular the question of whether the flesh parts of marble sculptures were originally painted or not. However, early doubts about the authenticity of the pigment traces led some twentieth-century scholars to question the authenticity of the sculpture as a whole.

For this study, the polychromy of the head was extensively investigated using non-invasive techniques (ultraviolet and visible-induced luminescence imaging) and invasive analytical methods, including Raman spectroscopy, Fourier transform infrared spectroscopy, high performance liquid chromatography and gas chromatography-mass spectrometry.

It was found that complex mixtures of pigments, and selected pigments for specific areas, were used to create subtle tonal variations. 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 colorant in the nostrils, the lachrymal ducts and the inner parts of the mouth; and red and yellow ochre for the hair.

The examination confirmed beyond doubt the authenticity of the preserved pigments and thereby the sculpture itself, which can now rightfully re-assume its important place in the art historical discussion of the polychromy of ancient sculpture. In addition, it provided valuable insights into Roman painting techniques on marble and allowed revealing comparisons to be made with other ancient polychrome works, such as funerary portraits.

 

Change and stasis: the technology of Dark Age metalwork from the Carpathian Basin
Paul Craddock, Michael Cowell, Duncan Hook, Michael Hughes, Susan La Niece and Nigel Meeks

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Summary
This is a comprehensive technical study of the British Museum’s important collection of material, principally from burials, belonging to the various groups who invaded and settled the Carpathian Basin of present day Austria and Hungary. These include the Huns, various Germanic tribes, Avars/Kezsthely and the Magyars, dated to between the fifth and twelfth centuries AD, together with some exotic material from contemporary Byzantine, Italian Lombardic and Carolingian cultures.

The items include jewellery of gold, silver and copper alloy, and display a wide range of composition and metalworking techniques. It is instructive to compare these with the contemporary alloys used in Byzantium, Western Europe and Central Asia.

The gold and silver items were mainly hammered to shape, whereas the copper alloy objects were almost all cast, even quite tiny pins. The copper alloys are usually of leaded bronze, reflecting traditions in central Asia stretching back to the Iron Age and in marked contrast to the contemporary material from the Mediterranean and Western Europe, which is usually of brass.

 

Investigating the construction methods of an opus vermiculatum mosaic panel
Melina Smirniou, Giovanni Verri, Paul Roberts, Andrew Meek, and Michela Spataro

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Summary
From the third century BC to the second century AD small detailed central panels (emblemata) made using the opus vermiculatum technique were used as focal points in larger mosaic pavements. They were custom made in stone or terracotta trays to facilitate their transport and placement. Although mosaic panels in opus vermiculatum have been discovered throughout the Hellenistic and Roman Mediterranean, the location of the workshops specializing in the production of these finely worked panels is still unclear. Their association with named artists, for example Dioskourides of Samos, and the location of finds (such as the fragment of the floor by Hephaistion at Pergamon), point to workshops in the Eastern Mediterranean.

A large unidentified fragment of an emblema, still in its terracotta tray, from the collections of the Department of Greece and Rome in the British Museum was the subject of analytical examination. These investigations of the tesserae (glass cubes), traces of pigments and mortar aimed to determine the raw materials and manufacturing processes for the mosaic and to characterize the nature of the application of paint to the mortar. Egyptian blue pigment and traces of hematite and carbon suggest that a fully coloured drawing was executed on the fresh mortar to guide the positioning of the tesserae. In addition, samples from the terracotta tray were taken in an attempt to identify its provenance. This contribution describes how the results of these investigations have been used to provide a deeper understanding of opus vermiculatum construction methods.

 

Assessing the effects of alkaline desalination treatments for archaeological iron using scanning electron microscopy
Melanie Rimmer and Quanyu Wang

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Summary
Archaeological iron objects are often vulnerable to severe post-excavation corrosion induced by chloride ions, a corrosion accelerator. To reduce this problem, alkaline deoxygenated desalination treatments may be used to remove chloride ions. There is very little information on the mechanisms and efficacy of such treatments and they are not in general use by British conservators. As part of a larger study, some iron objects were desalinated and a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectrometry (EDX) was used to analyze eight polished cross-sections of treated and untreated archaeological iron nails to investigate whether differences between treated and untreated nails could be detected with this method.

The analysis showed clear differences between the treated and untreated halves of the iron nails. Untreated nails showed regions of high chlorine content that appeared to be mobile and caused corrosion on the polished surfaces of the samples, despite storage at low humidity. Chlorine-containing corrosion products were identified as akaganéite using Raman spectroscopy. The majority of the treated samples showed no fresh corrosion or areas of very high chlorine content except near slag inclusions surrounded by metal. These caused fresh corrosion, presumably due to the inability of the treatment solution to reach these deep-seated areas.

The use of the SEM-EDX showed that desalination of the objects had a positive impact on the stability of archaeological iron. It also showed some of the limitations of desalination, such as its inability to remove deep-seated chloride ions. Although not an extensive study, this information is useful in understanding the effects of treatment on a detailed level and will complement existing data on the effectiveness of treatments.

 

Colour holography of the oldest known work of art from Wales
Hans Bjelkhagen and Jill Cook

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Summary
Dated as about 14000 years old, the jawbone of a horse decorated with zigzag patterns from Kendrick’s Cave, near Llandudno in North Wales, is the oldest known work of art from Wales. While it was on loan to Llandudno Museum as part of the British Museum’s UK Partnership Programme, the opportunity arose to reproduce it as a hologram using the most accurate currently available imaging technology. This contribution describes how the jaw fragment was reproduced using the latest techniques in three-dimensional colour holography, developed at the Centre for Modern Optics (OpTIC) at Glyndŵr University, St Asaph. The technique allows ultra-realistic colour images to be reproduced of the same size as the original. Using the horse jaw as a test case, the technique is described and the advantages of holographic reproduction, which include good three-dimensional image resolution, field of view and colour rendition, are outlined. Potential applications and limitations of the technique in archaeological research and museum outreach work are discussed.

 

New light on old swords from Iran
St John Simpson and Susan La Niece

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Summary
Iran is very rich in metal ores and has had an unbroken tradition of metalworking for at least 7000 years. At the end of the second millennium BC a number of regional cultures emerged within Iran, particularly in the north western and western parts of the country and these were particularly proficient in metalworking. Apart from a small number of stray accidental finds, the first occasion on which a significant number of such pieces entered Western collections – including the British Museum – was during the late 1920s. Almost all of these were acquired via the art market and lacked secure excavated provenances. This paper looks at two types of sword that have been scientifically examined with X-radiography, X-ray diffraction and X-ray fluorescence analysis. The results indicate that some swords with bronze hilts were certainly cast-on to bronze blades, but although some excavated examples show the casting of bronze hilts onto iron blades, many others circulating on the art market show unmistakable signs of having the corroded iron blades replaced by bronze blades from separate weapons of the same typological class. The results call into question some previous assumptions in the literature about swords of these types and underline the importance of using scientific techniques when analysing pieces purchased from the art market.

 


For more information about any of these articles contact science@britishmuseum.org
To order a hard copy of Volume 4 contact Archetype Publications: info@archetype.co.uk