High-tin Bronze Research Articles

한국 방짜기술의 출현과정에 관한 금속학적 연구: 국립경주박물관 부지 출토 통일신라 청동유물을 기준으로

한국 방짜기술의 출현과정에 관한 금속학적 연구: 국립경주박물관 부지 출토 통일신라 청동유물을 기준으로

Metallurgical traditions and metal exchange networks in late prehistoric central Myanmar, c. 1000 BC to c. AD 500

Myanmar has been notably underrepresented in recent studies of archaeometallurgy in Southeast Asia, despite its richness in both mineral and cultural resources and its potentially central role in long-distance exchange networks linking India, China and peninsular neighbours. Here, we present original analytical data on copper-base artefacts from several Bronze Age and Iron Age sites in Myanmar. Observed microstructures range from as-cast, worked, to fully annealed; compositions include leaded copper, low-tin to high-tin bronzes, and arsenical copper/bronze. Lead isotope analyses indicate that the metal originates from different geological sources, including several that match the lead isotope signatures of known prehistoric copper mines in Thailand and Laos. These archaeometallurgical data, including evidence for secondary copper-base production, more than double those currently available for Myanmar and document the presence of multiple local alloying and working traditions, perhaps chronologically differentiated, as well as identifying possible links to primary mineral sources across the region. Overall, this adds significant new information to the emerging picture of Southeast Asian prehistoric metallurgy at the crossroads of several major ancient cultures.

Indian High-Tin Bronzes and the Grecian and Persian World

This paper attempts to draw together some of the literary and archaeometallurgical evidence pointing to cross-cultural interactions and encounters in the use and occurrence of metals and alloys in the Indian subcontinent broadly in the 1st millennium BCE to the early common era, spanning the Iron Age to early historic period. As is generally known, aspects of the material culture of this period shows discernible external influences, such as from the Grecian, Hellenistic or Persian world, central Asia as seen in some examples of statuary, coinage and jewellery and so on. However, there are other examples which this paper aims to highlight of certain finds from the Indian context which seem to be more distinctive to the Indian region as also corroborated by evidence and accounts from the Hellenistic world. In particular the specialised alloy of wrought and forged high-tin beta (23%) bronze vessels provides an interesting case study, with the author’s archaeometallurgical investigations pointing to finds from the South Indian and peninsular Indian Iron Age of the early 1st millennium BCE (Adichanallur, Nilgiri, Mahurjhari, Taxila, Fig. 1), ranking amongst the earliest known such vessels, as well as continuing traditions (Srinivasan and Glover 1995, Srinivasan 2010). Some Southeast Asian examples of the latter part of the first millennium also show Indian connections in design suggesting an Indian provenance. Sassanian examples of about the 7th century are also known. This paper attempts to thus explore cross-cultural influences in the Indian examples, and the ways in which high-tin bronzes seem to have eventually become part of the wider Asian network of trade and interaction in antiquity.

Iron Age beta (23% tin) bronze: Peninsular Indian bowls of Adichanallur, Nilgiris, and Boregaon

ABSTRACTAs-cast binary copper–tin alloys with over 15% were generally not much in use in antiquity as they get embrittled at higher tin contents due to the increasing presence of the intermetallic delta phase compound. Even so, the unusual and skilled use of a higher tin binary bronze alloy, known as wrought and quenched high-tin beta bronze, is found, especially from some Iron Age or megalithic sites in southern and peninsular India, around the early first millennium BCE. They are closely approximating to the composition of the pure beta phase of 22.9% tin, which is an intermetallic compound. This article presents some of the micro-structural evidence of heavily hot-forged, carinated, and perforated bowls from the site of Adichanallur, Tamil Nadu. They rank amongst the most finely wrought examples of beta bronze known in the world, with continuing traditions into the medieval Chola Tamil region and contemporary period. A process of experimentation with thermomechanical processes in the Peninsular Indian Iron Age is also suggested, since it slightly differed from an example of a vessel with 21% tin that was only cast and quenched, found in Boregaon from the Vidarbha megaliths of Maharashtra in the Central Deccan.

Preliminary Investigation of Sri Lankan Copper-alloy Statues

The historical framework for the discussion is the chronology of Sri Lankan culture, which, based on the most recent archaeological evidence and radiocarbon dates, has been defined by three major periods: Early Historic (500 BC-300 AD), Middle Historic (300 AD-1200 AD) and Late Historic (1200 AD-1815 AD). A classification for the evolution of bronze sculpture with reference to the established historical chronology for Sri Lanka has been proposed by Reedy (2007) who sets out the following four major developmental periods of Late Anuradhapura (ca.432–993 AD), Polonnaruva (late 10th to early 13th century), Divided Kingdoms (13th to late 16th century), and Kandyan (17th to 19th century). This technical study investigated thirty sculptures including 25 tin bronzes in The Metropolitan Museum of Art and five from the Archaeological Department of Sri Lanka, representing all four major historic periods. The methods used to analyse the manufacture, composition, and condition of the statues were examination under magnification and Ultraviolet light, X-ray radiography, elemental analysis using X-ray fluorescence spectroscopy, and metallography. The results of the study included the finding that all the statues in the sample were cast using the lost-wax technique. Size does not seem to have had a bearing on whether statues were cast solid or hollow. Many of the small seated figures in the sample were solid cast, while a few were hollow cast. In addition the radiographs indicate that a variety of armatures of different thickness, size, and shape were present inside the hollow figures, irrespective of the size of the statues. Generally, metal of low porosity and few casting defects are observed in most of the radiographs, indicating that the castings are generally of good quality. Traces of five gates (or vents) observed on the backs of a group of five Lokapala figures examined, indicated that they were cast face-down in a horizontal position. Ten figures, particularly those from the later periods, show traces of gilding or intact gold layers. In all but one case, gold was found in association with mercury, confirming that they were amalgam gilded. Metallurgical studies were carried out on four figures in the sample: a Buddha, a Bodhisattva and two Hindu deities. A sample from a tang that was cast onto the goddess figure in antiquity proved to be quenched high-tin bronze, as evident from its microstructure; a tin content of 24.8 w/o was confirmed using X-ray energy dispersive spectroscopy in a scanning electron microscope. The four statues were from different historical periods and showed different microstructures, reflecting dissimilarities in composition, thermal history, and state of preservation.

High leaded tin bronze processing during multi-directional forging: Effect on microstructure and mechanical properties

The high leaded tin bronze alloy has been studied during multidirectional forging (MDF) process with differing crystallite size (D) in the scale of 240–90nm. The effect of MDF strain (εMDF∼ 0.25, 0.50, 0.75) after 3, 6 and 9 passes respectively on the development of homogeneity and refinement in terms of dislocation density, twin spacing, twin lamellae thickness and their division have been studied using high-resolution transmission electron microscopy (HRTEM) and micro-hardness measurements using Vickers micro-hardness. X-ray diffraction peak broadening investigation has revealed that the crystallite size decreases down to 90nm after 9 pass (εMDF∼ 0.75). The tensile fracture surfaces have been studied using scanning electron microscope (SEM) of received (AR) and MDF specimens. The results of crystallite size and dislocation density on the strength of refined microstructure and nanostructure have been correlated with mechanical flow stress.

Composition and microstructure of Roman metallic artefacts of Southwestern Iberian Peninsula

The Roman invasion introduces new alloys and metallurgical practices in Iberian Peninsula. The southwestern end of this region has many evidences of connections with the Roman World, but there are no studies about the manufacture and use of copper-based artefacts during this period. Therefore, a set of about 20 ornaments, tools and small attachments recovered at the Roman sites of Monte Moliao and Cidade das Rosas was studied by an analytical approach combining micro-EDXRF, optical microscopy, SEM–EDS and Vickers microhardness testing. The artefact composition shows a good correlation with function, namely pure copper for nails and rivets, low-tin bronze (2–6 wt% Sn) for basic tools, high-tin bronze (14 wt% Sn) for fibulae and high-lead bronze (19 wt% Pb) for a decorated jug handle. The manufacture also depends on function because most artefacts were subjected to thermomechanical processing, except the ornaments that would not benefit from post-casting work. Brass and gunmetal were only present in the site with a later chronology. A metallurgy visibly ruled by economical, aesthetical and technological concerns reinforces the evidences about the total integration of Southwestern Iberian Peninsula in the Roman World, but further studies will be essential to determine the evolution of copper-based alloys in Lusitania under Roman influence.

Improvement of bimetal joint quality in submerged arc surfacing of high-tin bronze on steel

Improvement of bimetal joint quality in submerged arc surfacing of high-tin bronze on steel

Nb<sub>3</sub>Sn 超電導線用高Sn ブロンズ中のTi 基三元化合物の挙動

High tin bronze is used as a component of practical Nb3Sn superconducting wires. In particular, the addition of titanium to bronze is well known to improve superconducting properties as well as the workability of the bronze alloy. In the present study, change in the microstructure of bronze by adding titanium was investigated. The important results are summarized as follows. First, when the Cu-10.5 at%Sn-0.72 at%Ti alloy was held at 550oC for 1000 min, three phases of primary α, γ and CuSnTi (Ti111) were equilibrated. Second, after holding at 750oC for 1000 min, three phases of primary α, β and CuSn3Ti5 (Ti135) coexisted. Third, during heating from 560oC to 750oC, a remarkable phase change was observed near 675oC, below which the Ti111 phase was dominant, but above which the principal Ti-based compound phase was Ti135. Fourth, in the present region of alloy composition and heat treatment temperature, two invariant reactions of Ti135 + β = α + Ti111 and α + β = γ + Ti111 were recognized to take place in the Cu-Sn-Ti ternary system. Finally, characteristic features of workability at room temperature as well as at elevated temperatures could be well explained in conjunction with the behavior of titanium ternary compounds.

Study of Microstructure, Mechanical Properties and Wear Rate of High Leaded Tin Bronze after Multidirectional Forging

In this work, the change in microstructure, mechanical properties and wear rate of high leaded tin bronze alloy was studied after multidirectional forging (MDF) process. The total equivalent strain of 0.75 was applied. During MDF process improved ultimate tensile strength, hardness and wear rate along with maintained ductility was reported. The initial average grain size of 120nm was refined to the final average grain size of 37nm. The transmission electron microscope, scanning electron microscope and optical microscope was used for microstructure observation of the sample without MDF, MDF and wear worn surfaces.

Investigations on interface microstructure and strength properties of dissimilar tin bronze/superalloy diffusion bonded joints

Abstract Diffusion bonding of dissimilar metals QSn4-3 and GH34 by using a QSn6.5-0.1 interlayer has been conducted in this study. The purpose of the study is to investigate the interface microstructure and strength of the joints, and to demonstrate the feasibility of using another high Sn content tin bronze interlayer to fabricate a typical microstructure joint. Microstructure examinations show that a penetration structure is formed by using a QSn6.5-0.1 interlayer, and its feature is apparent. Also, prolonging the holding time is conducive to the forming of the penetration structure. Shear testing results show that the penetration structure formed in a diffusion bonded joint of QSn4-3 and GH34 enhances the joint strength to almost the same as the QSn4-3 base metal. The mechanism forming the penetration structure is as follows: Sn atoms diffuse faster than Cu atoms into GH34 causing more Sn atoms to aggregate at the GH34 grain boundary. When the bonding temperature reaches 950°C for a short time, the aggregated Cu alloys having higher content of Sn than 5.3wt.% will melt, and penetrate and disrupt some grains from GH34 base metal.

Complementary use of X-ray methods to study ancient production remains and metals from Northern Portugal

Archaeological artefacts recovered at Castanheiro do Vento (Northern Portugal) were characterised by integrating macro and micro-energy dispersive X-ray fluorescence spectrometry (EDXRF) and scanning electron microscopy with X-ray microanalysis. The collection includes metallurgical remains (ceramic crucibles, a metallic nodule and a vitrified fragment) and metals (tools and ornaments) whose chronology spans from the Chalcolithic to the Roman Age. The study of production remains was able to identify distinct copper-based metallurgical operations including the smelting of copper ores, the melting of copper and tin and/or the melting of bronze scrap. Micro-EDXRF identified copper and arsenical copper tools as well as bronze and leaded bronze ornaments. The composition of tools (Cu with varying As contents: 0.46–3.6%) reveals an incipient technology, typical of the Chalcolithic till the Middle Bronze Age. On the contrary, ornaments are composed by different alloys – low tin bronze (4.8% Sn), high tin bronze (14.9% Sn) and high tin-leaded bronze (16.5% Sn and 2.4% Pb) − evidencing technological and economic choices that clearly indicate a late period such as the Roman Age. In conclusion, this multiproxy approach was able to study those ancient artefacts with a minimum impact on their archaeological and museological significance while providing important answers to the interpretation of the archaeological settlement and to better understand the metallurgical evolution in the Portuguese territory. Copyright © 2014 John Wiley & Sons, Ltd.

Thermographical Analysis of Continuing Tradition of Mirror Casting in Kerala

Additions of large amounts of tin to copper lead to high tin bronzes with interesting combination of properties. Such high tin bronzes need to be carefully processed to avoid brittleness in compositions corresponding to beta and delta phases. The latter has been used in China, India, Korea and Japan to produce distortion free mirror images. This investigation is concerned with the bronze mirror from India where the tradition has survived in the village Aranmula in Kerala. The alloy has an exceptionally high tin content consisting almost entirely of the delta phase, which is an intermetallic compound (Cu31Sn8) of composition 32.6% tin. This is an ideal alloy to be polished into a mirror due to the silvery white color and high hardness. Its high brittleness is offset by an ingenious casting and polishing process. In addition to studying the composition and the casting involving a mould cum crucible method, thermographic analysis has been employed to follow the solidification sequence by looking at the thermal profile. It is correlated with the actual composition, processing parameters and the resultant microstructure, due to the cooling rate the alloy solidifies with a mild departure from the equilibrium phase diagram. Some observations regarding the structure of the delta phase which is a Hume-Rothery phase will be provided about its optical and mechanical properties.

Investigation of Mechanical Properties, Microstructure and Wear Rate of High Leaded Tin Bronze after Multidirectional Forging

In this work, the change in mechanical properties, microstructure and wear rate of high leaded tin bronze material was studied after multidirectional forging (MDF) process. The total equivalent strain of 0.75 was applied during MDF process result in the improvement of ultimate tensile strength, yield strength, hardness and wear rate along with maintained ductility with the increase in the number of MDF pass. The initial average grain size of 120nm was refined to the final grain size of 37nm. The transmission electron microscope, scanning electron microscope and optical microscope was used for the microstructure study of the undeformed, MDForged and wear worn surfaces.

Megalithic and Continuing Peninsular High-Tin Binary Bronzes: Possible Roots in Harappan Binary Bronze Usage?

This paper attempts to trace the development of an unusual and skilled class of alloys, of binary high-tin bronze (i.e. alloys of only copper with a higher percentage of tin), which are found from surprisingly early contexts from Indian antiquity. In particular, the deliberate use was made of binary beta bronze with around 22–24 % tin, specifically exploiting the properties of higher hot-forgability of bronze of this composition due to the formation of the high temperature beta intermetallic compound phase of 22.9 % tin. Quenching resulted in the retention of the beta phase, yielding a musical alloy with golden lustre and improved tensile strength as compared to the as-cast state. Examples of hot forged and quenched high-tin beta bronzes studied by the author from the South Indian Iron Age and megalithic cultures from Tamil Nadu and Maharashtra and Gandharan Grave Culture of Taxila are summarised here ranking amongst the earliest and most finely wrought such finds. There are technological and morphological similarities to surviving high-tin bronze crafts practices documented by the author in Kerala since 1990. Since the 1990’s she has also documented the making of high-tin delta bronze mirrors at Aranmula with a composition closer to the pure delta phase of 32.6 % tin, which instead exploited the specular properties this alloy while managing its brittleness. Although it is difficult to speculate about origins, a long standing practice of using binary tin–bronzes (i.e. only copper–tin alloys) can be detected going back to Harappan bronzes which also seem to be predominantly binary bronzes with not much lead added to them. Though most of these seem to be low-tin bronze, the presence of a couple with higher tin of about 20 % is also notable in terms of the above discussion.

Bronze technology of the ancient megalithic communities in the Vidarbha region of India

Metallographic examination was carried out on forty-nine copper and bronze objects from five megalithic sites located in Vidarbha, India. The artifact assembly consists of horse ornaments, kitchenware, bangles, rings, small bells and the hilt of an iron dagger. Results show that the technology involved is characterized by the use of bronze alloys containing approximately 10% tin based on weight and the application of forging as a key method of fabrication. No deliberate addition of lead was observed. Arsenic was detected, but very rarely and only as an insignificant minor element. The consistent selection of such specific alloys indicates that the megalithic communities in this particular region had established a fully developed and standardized bronze tradition optimized for the production of forged items. Their advanced technological status was also noted in a special technique applied to two forged high-tin bronze bowls. Such a unique bronze tradition, dedicated to sheet metal technology, was most likely a practical choice made by these people to take advantage of the changing role of bronze. Specifically, with the introduction of iron, bronze seems to have become a more prestigious material that could serve as an indicator of the appearance of a more rigid socio-economic stratification within the megalithic communities of the Vidarbha region.

Copper quality and provenance in Middle Bronze Age I Byblos and Tell Arqa (Lebanon)

Forty-four Middle Bronze Age I weapons discovered at the sites of Byblos and Tell Arqa in Lebanon were investigated in order to study their copper quality and provenance. The evaluation of copper qualities is based on quantifying permanent inclusions such as copper sulfide and lead globules. The provenance of copper was studied using lead isotope analyses. For further discrimination between copper groups and sources elemental analyses by PIXE were performed on some of the weapons investigated. The results revealed two copper groups that could be qualified as “dirty” copper and “clean” copper. The former was used in most of the weapon types whereas the latter was reserved for items made of high-tin bronzes (>11 wt%) which underwent heavy hammering during the manufacturing process. Even though several potential copper sources were identified, the data point to Iran and Oman as the most probable areas of origin for the metal used in these weapons. These results contribute to the study of inter-regional exchange networks in the ancient Near East.

Micro-chemical and metallurgical study of Samnite bronze belts from ancient Abruzzo (central Italy, VIII–IV BC)

The Samnite bronze belts and the chest disk cuirasses (VIII–IV BC) are the distinctive defensive weapons of the Samnite warriors having likely also a symbolic relevance. These artefacts were mainly found during the archaeological excavations of warriors’ graves from ancient Abruzzo (central Italy). Their chemical composition, metallurgical features and corrosion products formed during the long-term burial have been studied by means of the combined use of analytical techniques such as optical microscopy (OM), scanning electron microscopy coupled with energy-dispersive X-ray micro-analysis (SEM–EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The micro-chemical and structural results show that the bronze belts have often been produced by using unusual high-tin bronze alloys achieving a silver-like appearance and by performing tailored cycles of thermal treatments under reducing conditions and hot mechanical working aimed to shape the high-tin alloys in the form of a thin bronze sheet. Furthermore, the investigation has shown that the main alloying elements have been transformed during the burial into mineral species giving rise to the formation of stratified structures constituted by different mineral phases such as tin oxides, cuprous oxide (Cu2O) and copper carbonates (azurite (Cu3(CO3)2(OH)2 and malachite (CuCO3Cu(OH)2)) as well as dangerous chlorine-based compounds such as nantokite (CuCl) and atacamite (Cu2(OH)3Cl) polymorphs. This information evidences the strict interaction of the alloying elements with the soil components as well as the occurrence of the copper cyclic corrosion as a post-burial degradation phenomenon. The present study confirms that the combined micro-chemical and micro-structural investigation techniques such as SEM–EDS, XPS, XRD and OM can be successfully used to investigate the technological production processes of the ancient artefacts and to achieve the detailed micro-chemical and structural description of the corrosion products useful for the identification of degradation agents and mechanisms and, thereafter, to propose a reliable tailored strategy for the conservation.

한국의 방짜유기에 가해지는 염수처리의 효과에 관한 연구

한국의 전통 방짜유기 제작과정에서 수행되는 염수처리가 가공 도중 유기 표면에 생성되는 흑색 산화막 제거에 유용한 것으로 추정되고 있으나 그 효과에 대하여 체계적인 연구가 수행된 사례는 찾기 어렵다. 본 연구에서는 염수처리가 청동기 제작에 미치는 역할을 밝히기 위하여 제작재현 실험과 성분분석 실험을 실시하였다. 먼저 유기공방에서 다양한 방법으로 염수처리 실험을 수행하였으며 여기에서 얻어진 결과를 바탕으로 실험실에서 자체 제작한 구리합금을 대상으로 두드림, 염수농도, 합금비율 등의 조건을 달리하며 다양한 실험을 수행함으로써 염수처리가 초래하는 효과를 밝히고자 하였다. 실험결과 염수처리를 통하여 고온에서 발생하는 산화막이 용이하게 제거되는 것으로 밝혀졌다. 이는 염수의 주성분인 염소(Cl)와 청동에 포함된 주석의 상호 작용에 기인하는 것으로 드러났으며 염수의 또 다른 성분인 나트륨(Na)은 산화막 제거에 별다른 영향을 미치지 못하는 것으로 판단되었다. 특히 한국의 전통 방짜유기 합금 조성인 주석함량 22%의 청동합금에서는 열간가공 수행 여부와 관계없이 염수처리를 통하여 산화막이 제거되었으며 이때 염수의 농도는 0.5% 이상이어야 효과를 볼 수 있는 것으로 밝혀졌다. 한편 납이 포함된 구리합금에서는 염수처리 효과가 나타나지 않았다. 이는 융점이 낮은 납이 녹으면서 시편 표면에 막을 형성함에 기인하는 것으로 추정된다. The brine treatment applied during the fabrication of forged high tin bronze objects is considered effective at the removal of surface oxide layers developed at elevated temperatures. There is not much information, however, available for the understanding of its exact effect and purpose. This work performed laboratory experiments to characterize the effect brine treatments produce on the surface of bronze objects during fabrication. Specimens were first made in the bronze shop of the Yongin folk village under varying conditions of brine treatments, and the results obtained were then used in the following laboratory experiments where the effect of brine treatments were investigated in terms of brine concentrations, alloy compositions and thermo-mechanical treatments. The results show that oxide layers generated at high temperature are easily removed by the brine treatment. It was found that the element, chlorine, played a key role in the removal of such oxide layers as opposed to the other constituent of the brine, sodium, makes no notable contribution. In bronze alloys containing 22% tin, this brine effect is obtained regardless of the application of forging as long as the brine concentration is over 0.5% based on weight. In alloys containing lead, however, no brine effect is observed due to the molten lead that emerges from inside the hot bronze specimen and forms a thin layer on its surface.

Techniques employed in making ancient thin-walled bronze vessels unearthed in Hubei Province, China

In this paper, two ancient thin-walled bronze vessels unearthed in Anlu County of Hubei Province, China, were studied systematically by using optical microscopy (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electron backscatter diffraction (EBSD) and nanoindentation system, and also we calculated the Sn diffusion in a Cu substrate based upon the substitutional mechanism at high temperature. The results indicated that the vessels were possibly fabricated using the following processes: (1) alloying the high-tin Cu–Sn bronze; (2) casting the preliminary shape of the vessels; (3) forging the vessels in the temperature range of 586–798 ∘C; (4) simply wiping tinning on the surface of the vessel at high temperature; (5) quenching the vessels to room temperature; and (6) at last, grinding and polishing the surface of the vessels. It seems that the present thin-walled bronze vessels provide an evidence of the spread of thin-walled high-tin bronze technology in China and its surrounding regions.