VII. Conservation and Analysis

The development of nontoxic, reliable, and long-lasting materials and the design of tailored methods for the conservation of bronze artworks are now professional mandates. The presently used hazardous materials and processes need to be replaced by environmentally friendly approaches due to the increasing importance of environmental protection and for the safety of professionals working in the conservation of cultural heritage.

Long-term stability of copper-based archaeological artworks is deeply affected by the nearly constant presence of chlorine in the corrosion layers that can induce the active cyclic copper corrosion known as “bronze disease.” The conventional conservation method applied to ancient bronzes uses a benzotriazole (BTA) alcoholic solution, which unfortunately is toxic and a suspected carcinogen. In order to reduce or overcome the toxicity of BTA, we adopted various tailored strategies of chemical research. Novel chemically synthesized and naturally derived products and suitable nanocarriers of corrosion inhibitors were purposely designed and tested by X-ray photoemission spectroscopy (XPS), scanning electron microscopy coupled with chemical analysis (SEM-EDS), optical microscopy, DC polarization, and electrochemical impedance spectroscopy (EIS).

Identification of the composition of “bronze” objects—many of which are not in fact bronze—is fundamental for studying the technology and intentions of the maker and the availability of tin and other alloys, and for providing accurate descriptive information for museum displays. There are many methods of elemental analysis, but most require the removal of a sample, which increasingly is not allowed for museum-quality objects. The use of a portable X-ray fluorescence spectrometer (pXRF) avoids this, but unfortunately provides results only on the near surface. Readings may be inaccurate due to heterogeneity caused by the cooling process, degradation/weathering, and cleaning or other preservation treatment.

In this study, a Bruker pXRF has been used to analyze hundreds of copper-based objects from different countries and many museums, and the advantages and limitations of this method are discussed in accordance with the research questions being addressed. These include (1) the initial technological transition from copper to arsenical copper and tin bronze alloys, and later to brass; (2) the availability of the secondary metals; and (3) analyses in American museums to assess authenticity and provide accurate descriptive information for display cases.

Thirteen ancient bronze artifacts coated with Incralac between 1976 and 2003 were examined using FTIR (Fourier transform infrared spectroscopy) and SEM-EDX (scanning electron microscopy coupled with energy dispersive spectrometry). The coated artifacts were selected as having no visible coating failure, and FTIR was used to determine whether there were any chemical changes to the coatings. The bronze objects are figurines, vessels, tools, jewelry, and mirrors, preserved at the National Archaeological Museum from many periods and places; and coins from the Epigraphic and Numismatic Museum in Athens, dating from the Hellenistic, Roman, and Byzantine periods. In parallel, Incralac was analyzed and tested on artificially aged coupons from six different distributors in Greece that sold the product to the museums between 1983 and 2002. According to the distributors, the product came from manufacturers in Italy, Australia, and the United States. The results showed that the Incralac formulation varied depending on the Greek distributor. Also, the long-term performance of the coating on the bronze artifacts was not always consistent. Some coated artifacts showed little chemical change after 25 years of coating, while others showed significant chemical change after just 15 years. FTIR was successful at detecting chemical changes to Incralac coatings not yet visible to the naked eye, serving as an early warning tool. Also, FTIR was able to verify the quality of product sold by Greek distributors.

The goal of the research is to find an alternative approach to stabilize chloride-contaminated copper-alloy artifacts, while retaining information preserved in the patina layers. Local electrolysis and the use of an alternative corrosion inhibitor, L-cysteine, were applied to treat bronze disease at specific locations on marine copper-alloy artifacts, while trying to preserve evidence of tinning on their surfaces. Cysteine as a nontoxic corrosion inhibitor has recently been tested and was found to be effective, but like all corrosion inhibitors, color changes to the patina can occur. Its application to intentionally tinned bronze surfaces was further investigated and combined with the application of local electrolysis using sodium sesquicarbonate to stabilize the areas where the surfaces are not covered with tin. The new approach was tested on a marine thirteenth-century copper-alloy cooking vessel excavated from a shipwreck found in the sea off the port of Rhodes in Greece. The approach was successful at stabilizing the object and no signs of active corrosion were visible one year after treatment.

The large equine protome from the Museo Archeologico Nazionale of Florence, called the Medici Riccardi horse head, has recently undergone conservation treatment sponsored by the Friends of Florence. The work was aimed at removing localized accretions and altered waxy layers. Materials were studied using traditional techniques and portable analytical devices, which identified hexogen materials, permitted their removal, and determined the composition of the underlying copper alloys. This maintenance intervention also provided an opportunity to extend the archaeometallurgical study carried out in the 1990s. The removal of the stratifications allowed a more accurate identification of the ancient repairs and modern integrations. A number of previously unknown cold plugs have been recognized, along with widespread traces of gold leaf, whose analysis unequivocally demonstrates that the artifact was originally gilded. Three-dimensional models of the outer and inner surfaces allowed examination of the thicknesses of the metal walls and careful mapping of surface features. The present conservation intervention improved the legibility of the artwork while the analysis of the data collected allows a thorough interpretation of its historical and archaeometallurgical aspects.

The Cleveland Apollo (Cleveland Museum of Art, inv. 2004.30) has continued to be the subject of extensive research since just prior to its acquisition in 2004. The life-size (H 150 cm or 59 in.) artwork depicts a youthful god of the sauroktonos type, including a small, serpent-like creature, now detached. The sculpture is nearly complete, missing only parts of both arms and the accompanying tree. This paper details the most recent research conducted in 2014 and, incorporating data from previous studies, provides a preliminary interpretation of the results. Research included extensive visual analysis, X-radiography, X-ray fluorescence spectrometry, metallography, and lead-isotope analysis of the bronze. These analyses had three primary goals. The first was to better understand the original manufacture, including how the indirect lost-wax bronze was cast, patched, and finished. The second aim was to reconstruct the history of the object before, during, and after burial. This included furthering the understanding of the bronze’s corrosion layers and remaining traces of archaeological materials, and also determining when and how the figure had been exposed to fire. Lastly, this research endeavored to elucidate decades of post-excavation display and interventions, including joining the sculpture to a bronze sheet as a display base, and reconstruction using modern materials.

Technical studies of the bronze Herm of Dionysos (J. Paul Getty Museum, inv. 79.AB.138) using microscopy, endoscopy, radiography, and tomography are summarized in the context of previous studies beginning in 1989. Internal rod remains may represent remnants of a casting sprue system and several areas of miscasting and larger repairs appear to be associated with the rods. Visible bronze spillage may be associated with reworking in the head drapery and suggests repair to the back of the head. Added materials include lead at the base, presumably from the original installation, as well as remains of a composite copper-and-marble eye assembly. Tomographic images taken at one height show some internal correspondences with the Mahdia herm (Bardo Museum, inv. F 107) although there are many dimensional discrepancies. This suggests the two herms may be associated generationally, but indirectly. The object’s surface alteration (from burial), bronze-alloy composition (previously reported), and lead-isotope data are consistent with ancient production.

Important advances have recently been made in the study of the Piombino Apollo, thanks to the rediscovery in 2010 of a fragmentary inscribed lead tablet with the partial names of two sculptors, initially found in the statue during the 1842 restoration ordered by the Louvre museum. The new results fully support the assumption of an Archaizing creation and moreover confirm the Rhodian origin of the statue. They allow us to propose a very narrow dating for its manufacture (120–100 BC) and to suggest that the statue was erected in the Rhodian sanctuary of Athena Lindia.

Such an accurate context is rarely achieved for an ancient large bronze statue. Henceforward, the Piombino Apollo may be regarded as an essential milestone for the knowledge of bronze manufacturing techniques in the Late Hellenistic period. Because technological data on the Piombino Apollo were lacking, a complete reexamination was undertaken. X-radiography, bulk-metal analyses by ICP-AES, and nondestructive analysis of the copper and silver inlays—by particle-induced X-ray emission (PIXE) with the AGLAE particle accelerator—were conducted in 2014, seeking specific technological markers of a Rhodian workshop at the end of the second century BC.

Following the cooperation initiated in 2012 between the Croatian Conservation Institute (HRZ) and the Centre de Recherche et de Restauration des Musées de France (C2RMF), the two institutions furthered their common investigation of the Croatian Apoxyomenos, a bronze male statue of the second or first century BC found in the sea in 1999. A new set of metal analyses was performed in order to clarify the alloy composition of the statue. In previous analytical campaigns, problems were encountered due to the heterogeneity of the metal and the heavy corrosion of the statue. We concluded that for a correct determination of the metal composition, a larger sample size was required. In addition, great care had to be taken to avoid inclusion of corrosion products in the samples, and that sample locations had to be chosen according to the results of a detailed investigation into the manufacturing technique of the statue.

We report here the results of the archaeometallurgical study of the bronze equestrian statuette of Alexander the Great, which was found broken in many pieces during various phases of excavation carried out in Herculaneum around the end of 1761; it was subsequently reassembled in the Royal Foundry of Naples. This famous masterpiece, now in the National Archaeological Museum of Naples, recently underwent a thorough material characterization, which was carried out during a static consolidation treatment at the restoration laboratory of Tuscany’s Archaeological Superintendency. This investigation was aimed mainly at interpreting the original execution processes and modern restorations. Although the authenticity of the artifact is supported by its formal coherence and archival information referring to the two figures (Alexander and his horse Bucephalus) and the base, analytical insights were considered of interest in order to assess the material coherence of the many fragments (about fifteen) composing the statuette. The results provide objective material evidence of the antiquity of most of the fragments and shed light on its ancient execution and modern restoration processes.

This paper summarizes preliminary results of an extensive, multidisciplinary conservation project at the Museum of Fine Arts, Boston (MFA) of a large cache of ancient musical instruments also known as “the auloi from Meroë.” The objects were discovered in 1921 during excavations by the Harvard University–Museum of Fine Arts Expedition of the burial site of Queen Amanishakheto (10 BC) in Meroë, Sudan. Multiple layers of tubing were recovered, consisting of exterior bronze sleeves encasing resonators of wood and bone. Due to the thin-walled structure of the objects, their exposure to long-term burial, and subsequent transport and handling, the pipes were fragmented virtually beyond recognition.

To date, the fragments have been documented and sorted, and many broken sections are now reconnected. Scientific examination of the materials included radio-carbon dating, identified textile fibers and wood types, and allowed insights into the complex nature of the metalwork.

Music-archaeological methods, combining the material evidence with the physics of ancient musical scales, have identified twelve individual pipes forming six pairs representing three different types of pipes, of varying length and with diverse mechanisms. The project’s long-term goal, in addition to physical reconstruction and stabilization of the ancient materials, is the fabrication of modern, functional replicas to discover the musical potential of these instruments.

The use of portable and handheld XRF analyzers has been widely adopted in metal compositional studies by cultural heritage professionals. However, studies have shown that the lack of certified reference materials and standardized quantification approaches has contributed to rather poor reproducibility of quantitative results among end-users in the analysis of historic and ancient copper alloys. The limited depth resolution of XRF analysis can impose additional difficulties for proper interpretation of analytical data obtained for ancient metal alloys, due to stratified corrosion layers at the metal-corrosion interface.

During the PROMET European FP6 project, a customized micro-XRF spectrometer was transported to the National Museum of Damascus, Syria, to study its unique bronze collection. Analyses were carried out on many important artifacts, such as Late Bronze Age gilded-bronze figurines from the site of Ugarit. The paper focuses on the micro-XRF analyses of two of these bronze figurines and highlights the methodological issues regarding the optimization and validation of the micro-XRF analytical approach for ancient copper alloys. The XRF analyses of these unique Mesopotamian figurines are presented with an emphasis on best practices for micro-XRF measurement protocols, data analysis, and interpretation.

Many different methods of analysis—art historical, technical, and scientific—must be considered at one time in order to determine the authenticity of an ancient metal artifact. But what should we do when multiple analytical methods are employed but no consensus can be reached? In this paper, we consider this question as applied to the Alexander Nelidow (inv. 1956.20), one of the most confounding and often questioned copper-alloy pieces in the collection of the Harvard Art Museums.

The piece has been examined and debated by art historians, conservators, and materials scientists for decades with no clear consensus having been reached about its authenticity. Thought by some to be a Roman-period copy of an original bronze statue of Alexander the Great created by Lysippos in the fourth century BC, the piece has also been attributed on stylistic grounds to the Renaissance. Although the surface of the statuette was stripped and partially recarved in the late nineteenth century, patches of thick cuprite remain in many areas. While the alloy is consistent with a Roman date (leaded bronze with only a trace of zinc), the lead-isotope composition is not consistent with known ancient ore sources.

In this paper, we discuss the sometimes conflicting results of the visual and analytical tests that have been conducted on the Alexander statuette. We compare these with results from other pieces in Harvard’s collection of equally uncertain date and of known replicas in order to achieve a better understanding of the different methods of authentication.

Two exceptional Greek original bronze statues were discovered underwater at Riace Marina (Calabria, Italy), in 1972. The statues represent a pair of warriors or athletes and are commonly labeled Statue A and Statue B. On the basis of stylistic studies, many authors date Statue A to 470–460 BC, and Statue B to 440–430 BC (Arias 1986).

During the restoration campaign carried out in Rome at the ICR, the inner cavities of the bronzes were explored and cleaned by remote-controlled mechanical arms. Here we report the archaeometric investigation of 12 metal samples taken from the inside of the statues: 3 bronze and 1 lead samples from Statue A; and 3 welding alloys, 3 bronze, and 2 lead samples from Statue B.

Chemical and textural investigation of the Cu-alloy samples was performed by SEM-EDS, EPMA, and metallographic analyses on polished cross sections. The data are discussed and compared with literature data available for coeval statues. Moreover, the lead isotopic compositions of selected samples were investigated by MC-ICP-MS. Comparison of the results with existing Pb-isotope databases (OXALID; BRETTSCAIFE.net; Alpine Archaeocopper Project) shows that the copper used for Statue A is compatible with western Mediterranean deposits, whereas the copper of Statue B fit with eastern Mediterranean ores. The isotopic signals of the welding samples from Statue B show a different provenance, possibly related to the age of the welding operations. The lead of the tenons of both statues has a very well defined isotopic signal compatible with a Greek source.

The fragmentary bronze statue (Louvre Museum, inv. Br 4388; 63.5 cm x 29 cm) was discovered in ploughed land near a rich Roman villa in Epiais-Rhus, northwestern France, which preserves the remains of a Gallo-Roman city. After being used as a flowerpot for some years, the statue was acquired by the Louvre in 1959 (Piganiol 1961, 295). A wing was discovered around the same area in 1977, which has been attributed to this statue and reattached to its back. The bronze sculpture depicts Eros as a baby; its prototype derives from a Hellenistic model (Mattusch 1996, 160–68). The Sleeping Eros type is rare among extant large bronzes: only few other examples are known, such as the remarkable Sleeping Eros in the Metropolitan Museum of Art in New York (Hemingway 2015) and a head from Volubilis (Boube-Piccot 1969, no. 174, 160–61, plates 90–92).

In order to investigate the manufacture and the dating of the Louvre’s statue, a technological study was carried out at the C2RMF. Study of the inner wall was eased by the open access at the back of the statue, and completed by X-radiography. Elemental composition was determined on micro-samples analyzed by PIXE. The statue appears to have been cast in nine separate hollow parts mainly by the indirect lost-wax process. A tin bronze with a high lead content (Sn: 7 wt%; Pb: 25 wt%) was used. The separately cast parts were then assembled using flow fusion welding or brazing, depending on the shape of the join (in basins or using a platform). Some other clues (such as fingerprints in the wax) helped to reconstruct each step of the manufacture with more detail and to qualify the Sleeping Eros from Epiais-Rhus as a large bronze statue elaborated during the second century AD.

This study compares analytical and methodological variations present in the copper alloys (bronze and brass) used to craft weapons (i.e., helmets, swords, spearheads) and ornaments (i.e., Classical Greek sculptures). IPCE’s Scientific Department made numerous analytic studies to evaluate the chemical stability and physical integrity of the artifacts. X-ray, XFR, and MEB-SEM were performed to determine composition and the presence of active corrosion.

The study is made by comparing pieces from various Spanish state museums, which have been analyzed and have undergone restoration and conservation during recent years by the Subdirectory of the Spanish Historical Heritage Institute.

Since ancient times, the discovery of fakes has been a hot topic: in the course of our scientific research we quite often discover interesting examples of ancient imitations of valuable items or coins. They give us a glimpse into what was considered precious at the time in which they were produced, and represent a welcome addition to our knowledge.

The discovery of modern fakes or forgeries (i.e., fraudulently altered ancient pieces) is a very different matter. Unrecognized fakes mar our perception of antiquity and must be identified and removed from the cases of our museums.

Identification studies of fakes are just as different and variable as the multitude of objects that come under our eyes while studying museum collections. In this paper, some of the most skillful ways of aging freshly made objects, for example, by applying some kind of a fake patina, are presented; “wrong” technical details are described; and several examples of ancient and modern fakes are discussed by highlighting their peculiarities.

This poster discusses the major issues related to modern studies on objects and materials of historical or cultural heritage. These usually involve the use of non-destructive and microanalytical techniques, which are employed for various purposes and particularly for cultural heritage. The conservation and restoration of materials and artifacts require analytical methods that can yield information on the chemical nature and composition of selected parts of artifacts to elucidate their provenance; on the state of alteration of the object as a result of short-, medium-, and long-term exposure to environmental conditions; and on the effectiveness of conservation strategies during and after application. This poster describes the application of non-destructive and microanalytical techniques to an ibis statue of the Late Period in Egyptian civilization, which was excavated from Tuna el-Gabal in Al-Minya Governate by Cairo University in 1946; the object is currently in the inorganic storeroom at Grand Egyptian Museum Conservation Center. It is obvious from visual examination and analytical techniques that the object was made from a variety of materials. Previous interventions showed contemporary support by the wooden base with iron pins and wire, and determined the nature of the corrosion product on the statue’s metal surface (identified by XRD analysis and SEM-EDS). The statue is missing part of a leg, and this poster will discuss possible and suitable ways to extend the statue’s life with safe and stable material (Plexiglas), which does not react with any material used in the artifacts of the ancient Egyptian civilization.

In the winter of 2005, an emergency archaeological excavation was carried out at the village of Chubtarash, in the Kargah Valley near the city of Khorramabad, western Iran. Some artifacts from the middle of the Parthian period (about first century AD) were found. The most important find of the excavation was a large metallic bathtub-like coffin in which a skeleton was found with two gold strips covering its eyes and mouth. The coffin has four handles that are joined to the tub-like body with pins. The coffin now is preserved in Falak-ol-Aflak Museum of Khorramabad.

To identify the manufacturing process of the coffin, a technical examination was performed by visual examination, SEM-EDS analysis, and optical microscopy (metallography).

The results showed that the coffin’s body is made of binary copper-tin (bronze) alloy. Other elements such as arsenic, lead, zinc, and nickel are detected as minor/trace elements. The handles also are made of tin bronze alloy, but with a different amount of tin. The observations and microstructural examination of samples revealed that the tub-like body of the coffin was manufactured in one piece, and a cycle of mechanical working and heat treatment was applied in order to shape the coffin. The bronze handles were made by casting, and some work was done on them to finish the final shape. The technical examinations on this individual bronze coffin from Iran illuminated some aspects of archaeometallurgical activities in the Parthian period of Iran.

The archaeometallurgical study of the metal artifacts is fundamental to their analysis and valorization. Material analyses and technological interpretations can contribute substantially to the revelation of cultural contents, which are complementary to historical and archaeological interpretations. Archaeometallurgy, in addition to reconstructing the history of objects’ technological development based on compositional and structural evidence, can allow discrimination between originals and replicas, recognizing possible integrations. It can also shed light on the creative process.

After about half a century of investigations into the manufacturing processes of ancient large bronzes, a great deal of material data has been collected on several masterpieces. However, the interpretation of the evidence and analytical measurements can sometimes be very complex, and results are often equivocal. Naked-eye observations, radiography, and some chemical analyses rarely permit the prompt determination of raw materials, crafting procedures of the wax model, core structure, casting setup, assembly, and finishing. On the contrary, thorough objective morphological and structural examinations, accurate compositional mapping, and very critical interpretation of the data are needed in order to reduce the range of the compatible technical interpretations. With the growing body of data comes an increasingly complex technological picture; some execution processes, which were once believed to be well-established practices in ancient times, today represent only a rather partial list of the methods used in Classical and Hellenistic art foundries.

Within this framework, the large bronzes of the Medici collections, exhibited at Florence’s National Museum of Archaeology, offer noteworthy examples of the methodological variability and of hitherto unknown peculiarities of ancient production, which significantly broaden the interpretational perspective. The Idolino from Pesaro (Iozzo 1998), the Minerva (Cygielman 2008) and the Chimaera of Arezzo (Siano et al. 2012; Siano 2013), the Arringatore (discovered in the environs of Lake Trasimeno), and the Horse’s Head (see essay 39 of this volume) have been thoroughly investigated during the last two decades. The present contribution discusses the main aspects of these studies along with their general implications in terms of methodological approach and knowledge of the ancient art foundry.