British Museum Technical Research Bulletin

Technical Research Bulletin Volume 3

Volume 3

Although all 13 articles in the third volume of the British Museum Technical Research Bulletin present research conducted in collaboration with the Department of Conservation and Scientific Research, the co-authors represent six of the eight curatorial departments in the Museum as well as other museums and universities in the UK and beyond.

Almost half the objects examined and conserved shed light on cultures from the ancient civilisations of Egypt, the Middle East and the eastern Mediterranean. Four articles present new findings on European gold coins, enamels, porcelain vessels and a rock crystal carving of a skull (although the last of these has sometimes erroneously been thought to be of ancient Mexican origin).

Treatment and analysis of a porcupine quillwork bag and Tahitian canoe sail show the value of detailed examination and conservation in revealing the hidden stories of objects – in these cases rare survivals of cultures changed irrevocably by contact with Europeans.

Finally, the volume is completed with a practical assessment of an issue faced by many institutions, how to deal with asbestos associated not with a building, but with the collection itself.

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

Articles

Sailing through history: conserving and researching a rare Tahitian canoe sail
Tara Hiquily, Jenny Newell, Monique Pullan, Nicole Rode and Arianna Bernucci

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Summary
The British Museum has a unique canoe sail in its collection, which is likely to be the only Tahitian canoe sail (‘ie) to have survived from the early era of sailing canoes. This sail is just over 9.5 metres long by 1.5 metres wide, curving at the top and bottom, and is characteristic of the Society Islands. It dates from either the eighteenth or early nineteenth century. It is constructed from finely plaited mats of cut pandanus leaf, with fibre loop fasteners secured along its edges, and has remains of the ropes that ran up each side of the sail and were used to tie it to a mast. Canoes and sails of this type were observed and documented by early European voyagers. Islanders and Europeans were fascinated with each other’s maritime technology and collected techniques and examples from each other. Several canoes and sails from the central Pacific were brought back to Britain and France in the eighteenth century and one of the richest collections of Polynesian maritime technology is held at the British Museum. In 2007 and 2008, the Museum’s Tahitian sail was assessed, conserved and documented in exceptional detail.

Conservation included the removal of soiling, crease reduction and the introduction of two types of support: lengths of toned mulberry paper were woven to support smaller, weak areas and holes, while strips of Tyvek were used to maintain plait alignment over large areas of loss, particularly during rolling and unrolling.

The collaboration between curators and conservators at the British Museum and a Tahitian curator was an important part of the conservation project and resulted in the creation of a large amount of information about this sail that now serves as a resource for a variety of interest groups, many from the Pacific, who are now able to access the sail without compromising its long-term preservation.

 

Limoges painted enamels: evidence for specialist copper-smithing workshops
Susan La Niece, Stefan Röhrs, Dora Thornton and Antony Simpson

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Summary
French enamellers active in Limoges during the late fifteenth to the early seventeenth century were noted for their fine painted scenes taken from classical mythology and Christian traditions. The forms made in the Limoges workshops included plaques, plates of various sizes, ewers and ewer stands, salt cellars, candlesticks and footed bowls, all of which were intended to be decorative rather than functional.

Instead of the more obvious painted enamel surfaces, this study examines the metalwork of these vessels.

The metal, entirely hidden beneath the enamel, is generally of sheet copper. While the study of damaged objects reveals constructional features, X-radiography of unaltered enamels, complemented by examination using a microscope and boroscope, has made it possible to understand the construction of the more complex shapes. The methods used to join the components are quite unlike those seen in sheet metalwork that was not intended for enamelling, and are partly explained by the need to avoid solder, which could not survive the temperatures of the multiple enamelling stages. The crudeness of the metalwork is in stark contrast to the quality of the enamelling and some very unusual and ingenious means were employed to conceal the mechanical joins in hollow feet. It is likely that the difficulties of the enamelling process led to many failures and rejects, making it uneconomical to invest time and effort in making the metal forms, although one common feature is that the metal was consistently kept as thin as practicable to minimize the adverse effects of differential expansion and contraction during firing and cooling. These observations lead to the conclusion that there were specialist metal workshops that were mass-producing copper forms specifically for enamelling.

 

Egyptian stelae from Malta
Jeremy Young, Marcel Marée, Caroline Cartwright and Andrew Middleton

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Summary
In 1829, four Egyptian stelae of Twelfth and Eighteenth Dynasty date were found, surprisingly, on Malta. Based on their far-flung findspot, some have suggested that the stelae were locally made by Egyptian colonists who had settled on the island during the second millennium BC. This contribution argues that the stelae offer no basis for such historical reconstructions. Style, content and petrology demonstrate that all four stelae were made in Egypt and that they originally stood in the necropolis of Abydos in Upper Egypt. Microfossils show that these stelae are made of Egyptian limestones, which are of a different geological age to limestones available on Malta. The examination of polished thin sections of samples from the stelae using scanning electron microscopy suggests that the limestones employed were quarried from four geological formations of different ages in the Nile Valley.

 

Analysis of a gold mancus of Coenwulf of Mercia and other comparable coins
Gareth Williams and Michael Cowell

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Summary
A gold mancus of Coenwulf, king of Mercia (ad 796–821), found in 2001, was subjected to material and stylistic analysis and compared to other Anglo-Saxon gold coins before its acquisition by the British Museum in 2006. Examination by scanning electron microscopy revealed that in common with the comparative coins, the Coenwulf mancus was die-struck, although its unusually well-preserved state revealed die preparation features not visible to the naked eye on the other coins. Analysis by X-ray fluorescence spectrometry showed that the coin was made from an alloy of gold, silver and copper with a high, but not exceptional, gold content. The high gold content may lie behind the lack of stress-corrosion cracking on the newly found coin. Stylistic analysis is consistent with coins struck from dies made by a die cutter who normally produced dies for Canterbury moneyers, although the coin was probably minted in London. Both the material and stylistic evidence suggest the coin is a genuine gold mancus of Coenwulf.

 

Early porcelain in 17th-century England: non-destructive examination of two jars from Burghley House
Michela Spataro, Nigel Meeks, Mavis Bimson, Aileen Dawson and Janet Ambers

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Summary
This contribution focuses on the investigation of seventeenth-century porcelain from the collection at Burghley House, Stamford, Lincolnshire, using non-destructive scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDX) and Raman spectroscopy. The glaze and body of three seventeenth-century objects, a small jar, its lid and a larger jar, were analysed by SEM-EDX using the variable pressure (VP) mode to allow the surface of the jars to be examined directly and without damaging these objects by the need to take samples. Both this new application of direct VP observation and analysis of ceramic vessels and the limits of the method are discussed, as well as the possibilities for obtaining results that are directly comparable to those acquired by standard methods that require intrusive sampling.

The EDX analyses of the bodies of the two jars suggest that they were produced using a similar paste, high in clay content, while analysis of the lid suggests that it was made using a different paste, perhaps at a different time or by a different artisan; this mismatch is supported by differences in decoration and the poor fit between lid and jar. The glaze analyses indicate variable concentrations of lead, which may partly derive from the pigments and variations in the thickness of the glaze. The pigments used to decorate the small and large jars were also studied by Raman spectroscopy, indicating the use of haematite.

The results from the two jars show that the porcelain is different to that produced at Fulham by John Dwight and in Dehua as ‘blanc de Chine’.

 

The manufacture of a small crystal skull purported to be from ancient Mexico
Margaret Sax and Nigel Meeks

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Summary
The small rock crystal skull (Am,St.420) was acquired by the British Museum in the 1860s and is possibly the earliest of several crystal skulls purchased by collectors in Mexico City between about 1850 and 1880, when interest in ancient Mesoamerican artefacts was high. To study the lapidary technology and authenticity of the Museum’s carving, scanning electron microscopy was used to investigate the manufacturing techniques and compare these with Mesoamerican lapidary practices in the pre-Columbian period prior to 1519. In contrast to securely dated Mesoamerican artefacts that were carved with hand-held tools, the small skull was predominantly worked with lathe-mounted rotary tools. Furthermore, the perforation had been modified and the surface appears to have been chipped deliberately, probably in imitation of antiquities recovered from burial. These observations suggest that the small crystal skull is a relatively recent piece of Mesoamerican skull art, made in post-Columbian times, between the late sixteenth century and the mid-nineteenth century when it was acquired.

 

Assyrian colours: pigments on a neo-Assyrian relief of a parade horse
Giovanni Verri, Paul Collins, Janet Ambers, Tracey Sweek and St John Simpson

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Summary
The colours present on a fragment of a neo-Assyrian carved stone relief (British Museum 1847,0702.27: ME 118831) depicting a parade horse, which retains extensive evidence of original polychromy, were investigated using visible-induced luminescence imaging and Raman spectroscopy. The horse harness was found to have been extensively painted with elaborate patterns including alternating bands of Egyptian blue and red ochre, two pigments commonly encountered in contemporary contexts. Although the blue pigment is still visible in some areas of the relief, its overall distribution across the object is obscured by surface dirt and/or the degradation products from the original materials. However, even in discoloured areas, the spatial distribution of the pigment was revealed by illuminating the object with visible light and by recording the luminescence of Egyptian blue in the infrared range (c.800–1000 nm). This non-invasive technique allowed the spatial distribution of Egyptian blue to be mapped thoroughly and rapidly.

The survival of some of the original polychromy on the relief poses constraints on its cleaning and raises questions about the survival of these and other pigments on Assyrian (and other) sculptures. However, the comparison of the distribution of pigments on this relief with that on contemporary Assyrian wall paintings from Til Barsib is highly instructive, as it confirms for the first time that similar colour schemes were used on reliefs and wall paintings.

 

A Great Lakes pouch: black-dyed skin with porcupine quillwork
Pippa Cruickshank, Vincent Daniels and Jonathan King 

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Summary
A late eighteenth-century North American pouch (1937,0617.1) represents an important type of a black-dyed skin bag decorated with porcupine quillwork. The pouch was made by women of the Ojibwa or Ottawa people and was probably used in medicine ceremonies. It came to the British Museum in the mid-twentieth century and when first examined in detail in the 1970s had already deteriorated. The skin has degraded due to the presence of a black dye, although an early watercolour painting of the bag discovered in the 1990s illustrates how the bag once looked. Black dyes containing both iron and tannin are well known to increase the rate of deterioration of many organic substances and the pouch was found to contain 1.63% iron. Experiments with a series of brain-tanned skin samples stained with various iron-tannin solutions and artificially aged showed that the presence of iron accelerated the deterioration of the skin.

A conservation treatment carried out in the 1970s, which included consolidation with soluble nylon and backing with nylon net adhered with an early thermoplastic adhesive, was no longer succeeding in keeping the bag intact, and further conservation was carried out to protect the 75% of the bag that survives. As the pouch is of a rare type it was decided to infill the missing areas to make it more suitable for display. The use of adhesives was kept to a minimum and solvent-reactivated adhesives were chosen in preference to those reactivated by heat. No further chemical stabilization was attempted in this treatment.

Bronzes from the Sacred Animal Necropolis at Saqqara, Egypt: a study of the metals and corrosion
Quanyu Wang, He Huang and Fleur Shearman

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Summary
More than 1800 bronze objects dating to c.600 BC were excavated from the site of the Sacred Animal Necropolis at Saqqara, Egypt between 1969 and 1971. While the important pieces had been accessioned by the Department of Ancient Egypt and Sudan and had been routinely cleaned using alkaline and/or acidic reagents in the 1970s, the residual group considered here, which includes numerous figurines and parts of sculpture, situlae and jewellery, had remained unregistered and uncleaned and so retained a burial corrosion crust. Both the metal substrates and the surface corrosion were studied to obtain information about objects that were under consideration for accession and to contribute to the wider study of this important site.

Microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry, X-ray diffraction and Raman spectroscopy were used for the microstructural and compositional analysis of metals and for the identification of the corrosion products on the surface. Of the five objects selected for metallographic study, two are tin bronzes and the others are leaded tin bronzes; four have as-cast structure while one (a ring) was cast and had been subjected to working and annealing. The pale blue corrosion on the surface was identified as a mixture of chalconatronite (Na2Cu(CO3)2•3H2O) and copper sulphates, with smaller quantities of acetates, including sodium acetate trihydrate and sodium copper carbonate acetate. Chalconatronite and copper sulphates are likely to be part of the original burial concretion, while the acetates have probably resulted from the alteration of the original corrosion and the formation of new corrosion in the presence of acetic acid during storage, as these objects have been stored in wooden trays since excavation. In the case of a composite bird figure, the wooden body of the object may have been the cause of localized formation of the acetates on the bronze foot.

In parallel to the scientific investigation, corrosion removal was carried out to reveal hidden decoration. Some of these objects have been cleaned and the unsuitable storage media have been replaced.

 

An unfinished Achaemenid sculpture from Persepolis
Tracey Sweek and St John Simpson

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Summary
During the conservation of an Achaemenid relief showing two grooms (British Museum 1825,0421.4: ME 118839) it was realized that the fragment had both a finished and an unfinished groom within the same carved panel. This relief is a fragment of part of the external façade of the north staircase of the monumental Apadana at Persepolis and dates from about 500–480 BC. A study of the carving marks on the finished and unfinished portions provided insights into the sequence in which the reliefs at Persepolis were carved and the tools used at each stage. The similarities and differences in the two figures illustrate the degree to which the individuality of the sculptor is evident in a scheme that was rigidly designed and laid out. The seemingly incomplete carving is also considered in the context of the vast scale of the carvings at the Apadana and the likelihood that the unfinished parts would have been masked, at least in part, by polychromy.

 

Scientific investigation of pottery grinding bowls from the Archaic and Classical Eastern Mediterranean
Michela Spataro and Alexandra Villing

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Summary
Pottery mortaria, or grinding bowls, are found in most early cultures around the Mediterranean. As with most plain, utilitarian household pottery, archaeologists often believe them to be locally produced and of too little value to be objects of trade. In order to test this view and to distinguish production centres and technological traits, petrographic analyses of thin sections and measurements of elemental composition using scanning electron microscopy with energy dispersive X-ray spectrometry were carried out on examples from several sites. These included pieces from recent excavations in the East Greek city of Miletos (Turkey) as well as from Al Mina in Syria, Lachish in Judah (Israel) and the Greek trading post of Naukratis in Egypt, all in the British Museum’s collections. In addition, several groups of reference material were analysed. Overall, 61 ceramic objects, mostly mortaria dating to the seventh–fifth century BC, were analysed. The results revealed that Cyprus was a major production centre for mortaria and that its products were widely traded in the Eastern Mediterranean, not only to the Levant but also to East Greece. The results also suggest further production centres, including locations in the Egyptian Nile Delta and at Miletos, and the use of different clay recipes in the production of the
same shape.

 

Establishing best practice in asbestos removal: the management of unique Medieval floor tile assemblages
Maureen Mellor and Denise Ling

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Summary
This paper outlines a proactive response by the British Museum to tackle a hazardous substance rather than leave it for a future generation to resolve. A total of 15 tile pavements and panels was removed from the former Medieval tile and pottery room (gallery 43), of which nine had been backed with ‘Asbestolux’ board, an insulation material that contains between 25 and 40% asbestos. These have been decontaminated, with three pavements and three smaller sections having been remounted for display in the new Medieval gallery. All nine are historically very important and unique artefacts, part of a collection of national and international importance; those chosen for redisplay exemplify different aspects and techniques of tile production and design. The technical challenges of ‘remote-control’ conservation through the walls of a protective tent are explored, including the training and monitoring of specialist contractors in conservation skills, while ensuring the safety of the staff. It gives a warning to others of the hazards of past practices, and sets out to show the Museum’s solution to the problem.

 

The Middle Bronze Age furniture from Tomb P19 at Jericho: wood identification and conservation challenges
Caroline Cartwright, Clare Ward, Jonathan Tubb and Hélène Delaunay

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Summary
Kenyon’s excavations of Tomb P19 at Jericho revealed wooden furniture and funerary artefacts of high quality that provide an accurate reflection of the esteem in which the individuals buried within it were held. Unusual conditions of desiccation had preserved the tomb’s organic materials, but upon excavation deterioration of the organic remains set in very quickly. Despite considerable problems for wood identification and the study of wood technology caused by deterioration during burial and brought about by the conservation methods and materials used at the time, particularly the liberal application of now-discoloured wax, a variety of timbers has now been securely identified. The most recent conservation assessments and treatments of the Tomb P19 wooden artefacts and furniture are described, including a preliminary assessment of the use of laser ablation to remove the disfiguring wax layer, and the implications of this study for the Jericho material on display in the British Museum are evaluated.

 

For more information about any of these articles contact science@britishmuseum.org
To order a hard copy of Volume 3 contact Archetype Publications: info@archetype.co.uk