Copper Alloy Objects Research Articles

Gold, Silver and Bronze Analysis of Three Fragments of Technical Ceramic from Elsfleth-Hogenkamp, Germany

Two crucible fragments were found during recent excavations in levels dated to the Roman imperial period in Elsfleth-Hogenkamp, a site interpreted to be a beach market located at the junction of the Hunte and Weser Rivers with water access to the North Sea. The crucible fragments were discovered in cultural layers dated to the 2nd-3rd centuries AD in an excavation trench placed near the concentration of metalworking debris, copper-alloy objects and casting waste found during terestrial metaldetecting surveys. Near this concentration in southwest part of the site, a fragment of technical ceramic with copper-alloy corrosion products was found as a surface find. These three pieces of technical ceramic were investigated by optical and scanning electron microscopy and compared with five pottery sherds of local manufacture. Evidence of the casting of gold, silver, bronze and copper was found as well as the importation of high quality technical ceramic. This study focuses on the material and technical aspects of the metallurgical ceramics and the results raise further questions on the meaning and organization of metalworking at the site.

Laser cleaning of copper in air and nitrogen atmospheres

We examine the physical and chemical processes occurring on the surfaces of copper and copper-alloy objects that are laser-cleaned using a Smart Clean 2 (El. En., Italy) pulsed YAG:Nd laser and a commercial MiniMarker2 M20 ytterbium pulsed fiber-optic laser, both with emission wavelengths of 1064 nm. We show that discoloration of the copper surface can be mitigated by performing the laser treatment in a nitrogen atmosphere.

The occurrence of brochantite on archaeological bronzes: a case study from Lofkënd, Albania

ABSTRACTA technical study was conducted on a group of copper alloy artifacts excavated from the burial tumulus of Lofkënd (fourteenth–ninth century BCE) to identify the alloy compositions and methods of manufacture. The surface corrosion was also examined in order to understand the diagenetic processes affecting the preservation of the finds and their condition. Portable X-ray fluorescence spectroscopy, metallographic examination, and X-ray powder diffraction (XRD) analysis were used to characterize the alloy composition and identify the corrosion products present. XRD analysis showed the presence of brochantite (Cu4SO4(OH)6) on five of the metallic artifacts. Brochantite is not commonly reported on archaeological bronzes from terrestrial sites, but is more readily found on copper alloy objects exposed to sulfur pollutants in the air or soil. The possible conditions that could have led to the formation of this corrosion on the bronzes from Lofkënd are discussed in the context of the particular burial environment found at the tumulus.

Iron Age tin bronze metallurgy at Marlik, Northern Iran: an analytical investigation

The archaeological excavations performed in 1961 and 1962 at the necropolis of Marlik (Gilan District, northern Iran) revealed important archaeological remains dating to Iron Age I and II periods (late second/early first millennium BCE). While the metal collection from Marlik includes various gold, silver and bronze objects and is considered one of the most significant finds of metal objects from the prehistoric Iran, the technological investigations discussed in this paper provide information on tin bronze objects only from Marlik. Both the composition and the microstructure of 25 copper alloy objects have been determined in order to achieve a better understanding of the metallurgical processes used in northern Iran from the second to the first millennium BCE. Experimental analyses were carried out using inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) and optical microscopy. The results demonstrated that the copper-base objects were made of the binary copper–tin alloy with variable tin contents. Other elements such as As, Ni, Pb, Zn and Sb were detected in minor/trace amounts. Variable tin content may be due to the application of an uncontrolled procedure to produce bronze alloy (e.g. co-smelting or cementation). Microscopic observations and microanalyses revealed the presence of numerous copper sulphide inclusions, lead globules and intermetallic phases scattered in the bronze solid solution. The microstructures seen in the bronze objects under study were varied and included worked/annealed or dendritic grain structures.

Prediction of the long‐term corrosion rate of copper alloy objects

Comparative atmospheric corrosion data for different metal alloys can be used to predict the service life of a component, maintenance requirements, and metal loss to the environment. In some international projects some prediction models have been derived for the atmospheric corrosion rate of metals – dose/response functions (EN ISO 9224, ECE UN ICP program, Multi‐Assess project) – including copper alloys.In this paper, actual corrosion studies of two long‐term exposed objects – a bronze statue of John of Nepomuk from Charles Bridge and the copper roof of Queen Ann's Summer Palace, are presented. Both these objects are exposed to Prague's urban atmosphere for more than 300 years. The predicted and measured corrosion rates are compared for these cultural objects. During their exposure the corrosion rates changed as the result of changing corrosivity of atmosphere in the Prague centre.

Chemical analysis of ancient Chinese copper-based objects: Past, present and future

The primary aim of this paper is to track the history of quantitative chemical analysis on Chinese copper-based metal objects and suggest a future outlook. The beginnings of this subject can be traced to the 1770s. Its overall history can be divided into five stages. By considering the different interpretational contexts in each of these stages, we show that all have made a significant contribution to our knowledge of the chemistry of copper alloy objects in China, and in broader terms to understanding the archaeology of China. Thanks to the sustained efforts of our predecessors, a substantial database of chemical and isotopic information has been created for present scholars, which we summarize here. We suggest, however, that this database contains a great deal of invaluable information which has yet to be fully explored. Moreover, given the scale of the Bronze Age in China, we also suggest that there is a great deal of more analytical work required before we can truly interpret the role of metal in Bronze Age Chinese society. This historical review also suggests that dialogue between related disciplines is a crucial factor in this area, and one which is vital in capitalizing the work already achieved.

Mis-cast and unfinished copper-alloy objects

Mis-cast and unfinished copper-alloy objects

A New Method For Combining Lead Isotope and Lead Abundance Data to Characterize Archaeological Copper Alloys*

We present a new methodology for interpreting lead isotope data from archaeological copper alloy objects. It is not based on the conventional isotope ratio biplots, which were originally devised to allow the calculation of the geological age of the lead mineralization, but is derived from isotope mixing models, more often used for presenting strontium isotope data. We illustrate the method by reworking published data on Sardinian Nuragic oxhide ingots and copper alloy artefacts. While we confirm the consensus assumption that the oxhide ingot fragments found on Sardinia are isotopically consistent with Cypriot copper ores (although we see no isotopic reason to favour only Apliki, as originally suggested), we also show that there is evidence for mixing between local and ingot copper in some objects, which was previously not detected. More broadly, we suspect that the apparent mismatch between some source allocations for copper drawn from isotope geochemistry and the rest of the archaeological data in some cases might be due to mixed isotopic signals being incorrectly assigned to a specific source, and suggest that the method presented here will reduce the chances of this happening.

Land and Sea Links: 1500 Years of Connectivity Between Southern Africa and the Indian Ocean Rim Regions, ad 700 to 1700

From the mid-first millennium ad onwards, southern Africa gradually became enchained to the Indian Ocean rim region, initiating over 1500 years of commodities and values exchange, which linked and transformed not just coastal regions but also their conjoined hinterlands in contrasting ways. Southern Africa and the Indian Ocean worlds had varying resource gradients which naturally stimulated conditions for trade and exchange relationships. Because of its strategic position, coastal east Africa acted as a conduit which enjoyed benefits from outbound and inbound commercial traffic. Whilst a lot of emphasis was traditionally placed on understanding the effect of Indian Ocean connections on coastal communities on the one hand, and hinterland communities on the other, little empirical research has focused on the links between individual coastal regions and their hinterlands. The implicit archaeological undercurrent is that the hinterland was always on standby to accept whatever the coast bestowed upon it—making every item of exotic origin a status icon in the interior. The popularity of commodities such as glass beads, cowrie shells and copper alloy objects, whose colours were compatible with preexisting cultural logics, when compared with the lack of popularity of imported ceramics, exposes that hinterland communities exercised a great deal of agency when accepting or rejecting inbound values and objects. Such selection processes account for why imported ceramics were popular on the coast but failed to appeal to interior populations, where local pottery was deeply wrapped up in transformation, theology and gender relations. This paper explores the archaeology of these processes and their consequences, from ad 700 to ca. 1700. It shows that whilst imports were incorporated into the hinterland value system, a great deal of continuity and change in selectivity forced the Indian Ocean world to stick to local tastes.

Terahertz pulse imaging in archaeology

The work presented in this paper was performed at the Oriental Institute at the University of Chicago, on objects from their permanent collection: an ancient Egyptian bird mummy and three ancient Sumerian corroded copper-alloy objects. We used a portable, fiber-coupled terahertz (THz) time-domain spectroscopic imaging system, which allowed us to measure specimens in both transmission and reflection geometry, and present time- and frequency-based image modes. The results confirm earlier evidence that THz imaging can provide complementary information to that obtainable from X-ray computed tomography (XRCT) scans of mummies, giving better visualisation of low density regions. In addition, we demonstrated that THz imaging can distinguish mineralized layers in metal artifacts.

Removal of brownish-black tarnish on silver–copper alloy objects with sodium glycinate

This article has the principal aim of presenting a new method of chemical cleaning of tarnished silver–copper alloy objects. The chemical cleaning must be harmless to the health, selective to tarnish removal, and easy to use. Sodium glycinate was selected for the study. The reactions of sodium glycinate with tarnish and the silver–copper alloy were evaluated. Products of the reaction, the lixiviated material, and the esthetics of silver–copper alloy coins (used as prototypes) were studied to evaluate if the proposed method can be applied to the cleaning of silver objects.Silver–copper alloys can be deteriorated through a uniform and superficial corrosion process that produces brownish-black tarnish. This tarnish alters the esthetic of the object. The cleaning of artistic and archeological objects requires more caution than regular cleaning, and it must take into account the procedures for the conservation and restoration of cultural heritage. There are different methods for cleaning silver–copper alloy objects, chemical cleaning is one of them. We studied two chemical cleaning methods that use sodium glycinate and sodium acetylglycinate solutions. Silver–copper alloy coins were artificially corroded in a basic thiourea solution and immersed in solutions of sodium glycinate and sodium acetylglycinate. After immersion, optical microscopy and scanning electron microscopy of the surfaces were studied. The sodium glycinate solution was shown to be very efficient in removing the brownish-black tarnish. Absorption spectroscopy measured the percentage of silver and copper lixiviated in immersion baths, and very small quantities of these metals were detected. Infrared absorption spectroscopy and X-ray fluorescence characterized the obtained products. The greater efficiency of the sodium glycinate solution compared to the sodium acetylglycinate solution was explained by chelation and Hard–Soft Acid–Base Theory with the aid of quantum chemical calculations.

Migration protocol to estimate metal exposure from mouthing copper and tin alloy objects

BackgroundLow blood lead levels previously thought to pose no health risks may have an adverse impact on the cognitive development of children. This concern has given rise to new regulatory restrictions upon lead metal containing products intended for child use. However few reliable experimental testing methods to estimate exposure levels from these materials are available.MethodsThe present work describes a migration test using a mimetic saliva fluid to estimate the chronic exposure of children to metals such as lead while mouthing metallic objects. The surrogate saliva medium was composed of: 150 mM NaCl, 0.16% porcine Mucin and 5 mM buffer MOPS, adjusted to pH 7.2. Alloys samples, in the form of polished metallic disc of known surface area, were subjected to an eight hours test.ResultsTwo whitemetal alloys Sn/Pb/Sb/Cu and three brass alloys Cu/Zn/Pb were tested using the saliva migration protocol. In the case of the whitemetal alloys, first order release kinetics resulting in the release of 0.03 and 0.51 μg lead/cm2 after 8 hours of tests were observed, for lead contents of 0.05-0.07% and 5.5%, respectively. Brasses exhibited linear incremental release rates of 0.043, 0.175 and 0.243 μg lead/cm2h for lead contents of 0.1-0.2%, 1.7-2.2% and 3.1-3.5%, respectively. The linear regression analysis of lead release rates relative to Pb content in brasses yielded a slope of 0.08 μg lead/cm2h%Pb (r2 = 0.92). Lead release rates were used to estimate the mean daily mouthing exposure of a child to lead, according to age-specific estimates of mouthing time behavior. Calculated daily intakes were used as oral inputs for the IEUBK toxicokinetic model, predicting only marginal changes in blood lead levels (0.2 μg lead/dL or less) for children aged 0.5 to 1 years old exposed to either class of alloy.ConclusionsThe results of this study as a whole support the use of migration data of metal ions, rather than total metal content, to estimate health risk from exposure to metals and metal alloys substances in children.

Species identification by peptide mass fingerprinting (PMF) in fibre products preserved by association with copper-alloy artefacts

Fibre products, such as textiles and animal pelts, are often recovered in the corrosion crust of archaeological metal artefacts. Because clothed burials are an important resource for the study of past societies, accurate fibre identification is important. However, extreme mineralisation of animal fibres can render microscopic visualisation difficult for species identification. Peptide mass fingerprinting (PMF) has been successfully used to identify the species origin in both collagen and keratin-made archaeological artefacts. The approach requires little material but the state of degradation (protein hydrolysis) is a limiting factor as it might impact on the identification of key markers. In this study we analysed pelt and textile fragments found in association with copper-alloy objects with different degrees of mineralisation; samples were obtained from a Viking-Age (10th c.) grave in Britain and from a burial in Mongolia (3rd c. BC to 2nd c. AD). Species identification was possible in all but one sample, revealing PMF can be applied to corrosion products, thereby further expanding the value of these objects for textile research.

Characterization and Evaluation of Salty Cleaning Compounds Study in Historic Objects made of Copper Alloys from the “El Tejas” Shipwreck

ABSTRACTRecent discoveries have shown the presence of several shipwrecks and historical pieces submerged in the seacoast of the Yucatan Peninsula of Mexico. Within these remains, it is common to found objects manufactured in copper alloys that were part of the construction system of the vessel. For the present study, different surface analysis techniques were applied to tubular copper alloy objects collected in the wreck “El Tejas”. The metallographic study allowed us to know not only the microstructure but also features over its manufacturing technique, as an example of nineteenth-century handmade production. SEM, EDX and XRF techniques allowed us know the elemental composition and establish the mechanisms of degradation of the different copper alloys in the seabed and evaluated a preservation method that consist on removing chlorine compounds by cleaning with pressure steam of distilled water.

A new interpretative approach to the chemistry of copper-alloy objects: source, recycling and technology

The metal composition of bronze alloys has been routinely examined as a means of inferring the source of the ore. But bronze is recycled, and the quantity of some components, such as arsenic, is depleted every time the alloy is melted down. Since the Early Bronze Age of the British Isles was largely supplied from a single mine on Ross Island, Co. Kerry, tracking arsenic content shows the number of re-melts and this gives the object a biography and a social context. Applying this ingenious new procedure to their large database, the authors also winkle out other sources of supply and new insights about the technology involved.

Sword and Dagger Pommels Associated with the Crusades, Part II: A Technical Study

The article discusses the results of a technical study of a collection of medieval sword and dagger pommels owned by the Metropolitan Museum of Art in New York City, with particular focus given to the probable use of the lost-wax technique to create them and the conclusion that they were most likely created in Europe due to the presence of Champleve enameling. A brief overview of medieval metalwork is presented, and the pommels and their creation are described in detail. The association of the pommels with the crusades is also commented on.

Alloys from Anau: The Manipulation of Metallic Properties in 3rdMillennium B.C. Southern Central Asia

ABSTRACTMetallography, chemical analysis, and microhardness testing of copper-alloy objects from Anau, Turkmenistan (c. 3000-2400 B.C.), were undertaken to determine how technological choices influenced the properties of the finished objects. Additionally, this analytical program assessed the position of the Anau metals in the development of metallurgy in southern Central Asia. Metallographic analysis of three bladed objects, all copper-arsenic alloys with 1% to 5% arsenic, showed that their edges had been cold-worked to a greater or lesser degree to create a blade that maintained a sharp edge, but also had flexibility to withstand impacts. Microhardness testing confirmed that the blade edges had a higher hardness than the interior metal. One of the objects had sulfur-rich inclusions in the metal matrix, suggesting the original charge had at least some sulfide ore. Conversely, a curved rod, made from a copper-lead-tin alloy, was cast to shape and showed no additional working of the metal. Lead, visible as black particles in the microstructure, was likely added to make the molten metal flow more easily. The metallographic and chemical analyses showed that the Anau objects fit into the tradition of Southern Central Asian metallurgy, though the presence of tin in objects of this period is more rare here than in later periods. Anau smiths displayed an ability to manipulate both physical and chemical properties of metal in order to produce functional objects with optimal characteristics.

Later prehistoric settlement and metalworking site at Seafield West, near Inverness, Highland

Construction in 1996 at a major retail development site close to Inverness, Highland (NGR: NH 694 445) resulted in the destruction of two known cropmark sites. One set of cropmarks was found to be associated with a Bronze Age log-boat burial site and the results of the ensuing excavation are published elsewhere (Cressey & Sheridan 2003). The excavation of a second area of cropmarks forms the subject of this publication. The archaeological remains consisted of a series of negative features, post-holes and annular ditches which form parts of at least nine separate structures of a later prehistoric unenclosed settlement. A mould fragment indicated Late Bronze Age sword production in the vicinity. A palisaded enclosure produced a copper-alloy brooch that is a rare find for the region. Evidence of copper-alloy objects and metalworking from a smelting hearth and slags show that the occupants were of some status. Some of the structural and artefactual evidence compellingly points to an in situ ironworking workshop. A large cache of smithing charcoal found in association with a smelting hearth was radiocarbon dated to 180BC–AD70 and represents one of the few dated in situ Iron Age ironworking episodes in Scotland.

A Later Prehistoric Settlement and Metalworking Site at Seafield West, near Inverness, Highland

Construction in 1996 at a major retail development site close to Inverness, Highland resulted in the destruction of two known cropmark sites. One set of cropmarks was found to be associated with a Bronze Age log-boat burial site and the results of the ensuing excavation are published elsewhere (Cressey & Sheridan 2003). The excavation of a second area of cropmarks forms the subject of this publication. The archaeological remains consisted of a series of negative features, post-holes and annular ditches which form parts of at least nine separate structures of a later prehistoric unenclosed settlement. A mould fragment indicated Late Bronze Age sword production in the vicinity. A palisaded enclosure produced a copper-alloy brooch that is a rare find for the region. Evidence of copper-alloy objects and metalworking from a smelting hearth and slags show that the occupants were of some status. Some of the structural and artefactual evidence compellingly points to an in situ ironworking workshop. A large cache of smithing charcoal found in association with a smelting hearth was radiocarbon dated to 180BC-AD70 and represents one of the few dated in situ Iron Age ironworking episodes in Scotland.

Near Eastern ancient bronze objects from Tell Beydar (NE-Syria): insights into their corrosion

T site of Tell Beydar is located in north-eastern Syria, somewhat 30 km north of the modern city of Hasake, along the river Khabur (Figure 1) [1]. The history of Tell Beydar starts with the foundation of Nabada, its ancient name, around 2800 BC. Semitic nomad tribes were most probably the founders of this city. A palace was built around 2500 BC and the city passed through a period of great prosperity. At the end of the 25th century BC Tell Beydar was placed under the reign of the kingdom of Nagar (Tell Brak), whose king was visiting Nabada at regular periods in order to participate in certain religious and political events. The city was dominated by Akkadian oppressors during the Akkadian period (2350-2200 BC) and was finally abandoned. The lower parts of the city were again inhabited in 1500 BC by the Mitanni. In the 7th century BC Assyrians built their homes at Tell Beydar. Again Tell Beydar was departed until the Seleucidians and Parthians started to inhabit the upper town in the 4 century ad [2]. Excavations at Tell Beydar have been conducted by a European-Syrian mission under the direction of the European Centre for Upper Mesopotamian Studies in Brussels [3]. All of the bronzes discussed in this work (twenty in total) were excavated during the 1994, 1998 and 1999 field seasons. The samples date to the Early Dynastic II-III period (2700-2300 BC). In a preceding study, chemical analysis and metallographic examination of a set of copper alloy objects were performed [4]. The objective here was to identify the metals used at Tell Beydar during different periods of occupation. Drawings of the objects are shown in Figure 2. Results showed that four different compositional groups could be distinguished based on their arsenic and tin content: a low arsenic group (As 2 w%),an intermediate tin group (Sn between 3 w% and 6 w%) and a high Sn group (Sn> 7 w%). Moreover a clear chronological sequence in the use of copper alloys at Tell Beydar could be observed. Throughout the EDII period (2700-2600 BC) low and high arsenical bronzes were in use simultaneously, while there is clearly no evidence of the presence of tin bronzes. Later, during the EDIII period (2600-2300 BC), tin bronzes come into use and the presence of high arsenical bronzes ceases. Finally during the Akkadian (2300-2200 BC) period results show that both tin bronzes and high arsenical bronzes are no longer present. The fact that Tell Beydar was part of another kingdom during this Akkadian period is a possible explanation for the disappearance of the tin bronzes. Later on, during the Seleucid and Parthian occupation (400 BC – 200 AD), tin bronzes appear again in the metal repertoire of Tell Beydar. Apart from these conclusions the results also indicated that the studies of Tell Beydar bronzes have possibly a different provenance. The study of the microstructure revealed that, in general, the same basic working techniques were used during the period studied. Basically the rough shape of the object was formed by casting the liquid metal into a mould. The object was hammered into shape, both cold and hot, after cooling down. Although it is clear that the same basic methods were used throughout the various periods, the evolution of the microstructure shows that metal smiths were achieving better control over the process of cold and hot working the metal. At the end of the development period the metal smith knew how to create objects having the same composition but with different properties, especially hardness.