Rui J . C . Silva

This study is part of a wide-scale research on metal production in SouthWestern al-Andalus during the Islamic period, under the project "DE RE METALLICA-DEfining and REdiscovering MEtallurgy and Trade in AL-Andalus (8th-13th centuries AD): Leaping into Innovative Comprehensive Archaeomet-ric Approaches". In particular, this paper presents the results of the elemental analysis carried out on a group of six Islamic oil lamps found at different sites in Southern Portugal, spanning from the 10th to the 13th centuries AD. Due to the exceptional historical value of these artefacts, the analyses were carried out according to a completely non-destructive approach that combines Energy Dispersive X-ray Fluorescence Spectrometry (EDXRF) with a Monte Carlo (MC) simulation code named X-ray Monte Carlo (XRMC). This novel and groundbreaking approach has proven to be especially suitable for non-destructive analysis of artefacts with a multi-layered structure, such as archaeological metals, being able to estimate the composition of the original alloys and to characterise the structure and composition of each layer superimposed to the bulk with no need of removing samples or cleaning the artefacts' surface from corrosion compounds. The application of the EDXRF/MC analytical protocol revealed that the six oil lamps selected for this paper are covered by a structure composed of three different layers (protective layer + corrosion patina + alloy). The bulk metal is a copper-based alloy with a great variability in terms of Fe, Zn, Sn, As, and Pb, likely suggesting either the use of scrap metals as raw material or the indiscriminate addition of different kind of minerals. With regard to the objectives of this paper, EDXRF/MC protocol successfully allowed to estimate the chemical composition of the six oil lamps in a completely non-destructive way, thus representing a viable compromise between the necessity to ensure their physical integrity and the need to obtain reliable analytical data able to address historical issues.

The circulation trading routes and the characterization of the silver metal used in the European continent in the 15–17th centuries are historical issues that are still open. This study aimed to bring an insight into the silver processed within a chronological framework in the Portuguese territory, relating the analytical data with the known historical information. This investigation developed on 230 high silver coins from two important Portuguese coin collections was based mainly on surface particle-induced X-ray emission (PIXE) analysis, complemented with a few energy-dispersive X-ray fluorescence (EDXRF) analyses. The silver processed in different timelines was discriminated based on the variation of the impurity contents, namely Au and Bi. European silver with high Au and Hg and low Pb and Bi contents supplied the 15th century chronologies, being replaced at the dawn of the 16th century by a new metal entering the Portuguese capital. This new metal, with low Au and high Bi contents, was probably derived from European argentiferous copper ores. By the end of the 1500s, the Philippine chronologies reveal the newly discovered Potosí silver, identified for the first time based on PIXE minor and trace element surface contents, distinguishable from the European silver in use until 1578 in the Portuguese territory, by Au contents <100 ppm and very low Bi contents.

A collection of 35 metallic artefacts comprising various typologies, some of which can be attributed to the Bronze Age and others to later periods, were studied to provide detailed information on elemental composition, manufacturing techniques and preservation state. Elemental analysis by micro-EDXRF and SEM–EDS was performed to investigate the use of different alloys and to study the presence of microstructural heterogeneities, as inclusions. X-ray radiography, optical microscopy and SEM–EDS were used to investigate manufacturing techniques and degradation features. Results showed that most of the artefacts were produced in a binary bronze alloy (Cu–Sn) with 10–15 wt% Sn and a low concentration of impurities. Other artefacts were produced in copper or in brass, the latest with varying contents of Zn, Sn and Pb. A variety of inclusions in the metal matrices were also found, some related to specific types of alloys, as (Cu–Ni)S2 in coppers, or ZnS in brasses. Microstructural observations revealed that the majority of the artefacts were subjected to cycles of thermomechanical processing after casting, being evident that among some artefacts different parts were subjected to distinct treatments. The radiographic images revealed structural heterogeneities related to local corrosion processes and fissures that seem to have developed in wear-tension zones, as in the handle of some daggers. Radiographic images were also useful to detect the use of different materials in one particular brass artefact, revealing the presence of a possible Cu–Sn solder.

Provenance and production of tin in the Ancient World has since long been a major topic of discussion among archaeologists. In Western Europe, where significant tin ore (cassiterite) deposits are known, only a few remains of ancient tin production, such as tin slags, have been detected. In the present work, elemental and microstructural analyses by WDXRF, SEM-EDS and XRD were performed on recently recognised tin slags from the Iron Age Carvalhelhos hillfort located in NW Iberia, a territory that represents the largest extension with tin mineralisation in Western Europe. Elemental and microstructural characterisation of cassiterite collected in a pilot field survey in the region of the hillfort are presented and discussed, as well as two ceramic fragments that could be part of a smelting structure and an iron slag from the settlement. Results show that the tin slags have variable but high contents in Sn, similarly to Pre-Medieval tin slags found in other Western European areas, but also high contents of Ta and Nb, which specifically distinguish them from other tin slags, such as those found in SW Britain. Tin ores from the hillfort region frequently have Ta and Nb in cassiterite solid solution or as inclusions of columbite group minerals, relating well with the Carvalhelhos tin slags. Up to present, the Carvalhelhos slags are amongst the very few ancient tin slags known in Western Europe, and their study can contribute to a better knowledge on ancient tin sources and trade routes.

Abstract. Ga-doped polycrystalline zinc oxide (GZO) thin films have been deposited at high growth rates by rf magnetron sputtering. The dependence of electrical, optical and morphological properties on the rf power density were investigated. The lowest resistivity ...

COMENDADOR REY, B., MEUNIER, E., FIGUEIREDO, E., LACKINGER, A., FONTE, J., FERNÁNDEZ FERNÁNDEZ, C., LIMA, A., MIRÃO, J. et SILVA, R. J. C., 2017, « Northwestern Iberian Tin Mining from Bronze Age to Modern Times: an overview ». In : Newman, P. (Ed.), The Tinworking Landscape of Dartmoor in a European Context. Sowton, pp. 133-153.

The northwestern Iberian Peninsula has been well known for its mineral wealth since classical times, including for gold and for tin. In fact, the Iberian tin belt is the largest in western Europe (covering an area of c.200,000 km2), containing tin deposits that were accessible from ancient times. Nevertheless, few archaeological studies have been dedicated to ancient tin mining in the region, unlike gold mining, for which major mining complexes are known from Roman times (e.g. Las Médulas, N Spain, and Três Minas, N Portugal). In this paper, evidence for tin mining in different periods, from Bronze Age to modern times, is discussed, based on selected case-studies, using various approaches developed for the study of ancient and modern tin mining, by members of the present Iberian Tin Research Group. An introduction to the geographical and geological contexts of Iberian tin, and the history of investigation on Iberian tin mining, is included.

Archaeological materials present unique records on natural processes allowing the study of long-term material behaviors such as structural modifications and degradation mechanisms. The present work is focused on the chemical and microstructural characterization of four prehistoric arsenical copper artifacts. These artifacts were characterized by micro-energy dispersive X-ray fluorescence spectrometry, optical microscopy, scanning electron microscopy with X-ray microanalysis, micro-X-ray diffraction and synchrotron radiation micro-X-ray diffraction. Cu3As is the expected intermetallic arsenide in arsenical copper alloys, reported in the literature as exhibiting a hexagonal crystallographic structure. However, a cubic Cu3As phase was identified by X-ray diffraction in all of our analyzed archaeological artifacts, while the hexagonal Cu3As phase was clearly identified only in the artifact with higher arsenic content. Occurrence of the cubic arsenide in these particular objects, suggest...

ABSTRACT The Castro of Vila Nova de São Pedro (VNSP) is an emblematic settlement located at Azambuja, Portuguese Estremadura. It was occupied during the third and second millennia BC, predominantly during the Chalcolithic period. A diversified collection of 53 copper-based artefacts (most part in a fragmentary condition), belonging to an extensive metallic collection recovered during excavations carried out in VNSP, was studied using micro-EDXRF spectrometry, optical microscopy and SEM-EDS. Additionally, Vickers microhardness measurements were performed to establish the effectiveness of the thermomechanical treatment in the hardness of the artefacts. Results show that the Largo do Carmo, artefact collection is mainly composed of copper or arsenical copper, being 37% of the artefacts made of copper alloyed with arsenic (As &amp;gt; 2%). A statistically significant association was found between copper alloyed with arsenic and artefacts classified as tools/weapons (arrowheads, daggers and knives). In several cases, the presence of arsenic rich phases in the microstructure, resulting from an inverse segregation phenomenon, shows no evidence of chemical homogeneity control during the artefact manufacture. Microstructural analyses also show that the majority of this group (73%) was shaped with forging plus annealing operation cycles and 23% of the artefacts received a final cold hammering after the forging and annealing. An association between the presence of a final forging treatment and artefacts presenting higher arsenic contents was also identified. Nevertheless, no direct correlation was found between the arsenic content of the alloy and its hardness. Also no direct correlation was found between the hardness and a final forging operation. However, it was observed that a harder forging was applied to the cutting edge of the artefacts and consequently a high hardness in this area was obtained despite the arsenic content of the alloy. Concerning arsenical copper alloys, all evidences point out that the potential for obtaining a harder material was not recognized by the ancient metallurgists and the selection of the alloy was possibly made based on colour.

ABSTRACT The Castro de Vila Nova de São Pedro (VNSP) is an emblematic settlement located at Azambuja (Portugal), occupied predominantly during the Chalcolithic period. A large and diversified metallurgical collection was recovered from this settlement which includes artefacts, crucibles and other metallurgical production remains, like slags and droplets. The chemical and microstructural characterization of this metallic collection aims to contribute to a better comprehension of the early copper-based metallurgy on the Portuguese Estremadura, the degree of knowledge of the ancient metallurgists and the role of the metallurgical activities in Chalcolithic societies.A group of 53 selected copper-based fragments of artefacts plus metallurgical production remains (12 crucibles and 20 slags and droplets), all belonging to VNSP, were characterized by using different analytical techniques: EDXRF and micro-EDXRF spectrometry, optical microscopy (OM) and SEM-EDS. The EDXRF and micro-EDXRF spectrometry gives the elemental composition of the artefacts and metallic nodules. The microscopy techniques play a fundamental role in the chemical and microstructural characterization of artefacts and metallurgical remains. The OM allows the identification of different phases, inclusions and thermomechanical processes applied during the shaping of the artefacts. The SEM-EDS plays an important role in the determination of main chemical phases present in the metal alloy and slags, and also in the distribution of chemical elements and minerals in the inclusions. The combination of these two microscopy techniques gives indication of the processes used in the reduction of minerals in order to obtain the metal and also allows the characterization of the operation chain, regarding the production of artefacts.The research that has been carried out by us offer indications concerning the provenance of the arsenic, the technological choices involved in the production of an arsenical copper alloy and how it was recognized by ancient metallurgists. Results obtained on the elemental composition of the metallurgical production remains are consistent with copper and arsenical copper (As &amp;gt; 2 %) artefact production. Crucibles and slags analysed indicate melting and smelting operations (of copper ores or copper/arsenic ores). A statistically significant association was found between copper alloyed with arsenic and artefacts classified as tools/weapons (arrowheads, daggers and knives). In several cases, the presence of arsenic rich phases in the microstructure, resulting from an inverse segregation phenomenon, shows no evidence of chemical homogeneity control during the artefact manufacture. Microstructural analyses also show that the majority of the artefactual group was shaped with forging plus annealing operation cycles and 23 % of the artefacts received a final forging treatment. This final treatment was associated to artefacts presenting higher arsenic contents.This research work has been financed by the Portuguese Science Foundation (FCT-MCTES) through the EarlyMetal project (PTDC/HIS-ARQ/110442/2008) and the PhD Grant SFRH/BD/78107/2011 (FP). The financial support of CENIMAT/I3N through the Strategic Project-LA25-2011-2012 (PEst-C/CTM/LA0025/2011) is also acknowledged.

In the present work microstructural and chemical analysis of tin and slag that resulted from three smelting experiments reconstructing prehistoric conditions are presented. Cassiterite ores were collected from NW Iberian deposits and were smelted in a small open pit. Results show that the loss in tin can be very high, up to 80%, mainly as a result of volatilization of Sn species. The experiments show that using handmade leather bag bellows and clay tuyeres, temperatures can easily reach >1200°C. The tin produced was a very pure (Sn) solid solution, with the presence of dispersed inclusions or phases of various composition. These included FeSn and FeSn2 intermetallics and small metallic W inclusions. Slags could be grouped into three types based on their physical characteristics, and bulk chemical analysis could relate each type as being a product from the reaction of ore material or a product from the reaction with the crucible material. Generally, it was found that in spite of very low recovery rates, the tin produced by this simple technique would have been adequate for a domestic small-scale production.

A collection of 54 bronze artefacts recovered from the inland settlement of Castro dos Ratinhos (Portugal) and belonging mainly to the 9th–8th centuries BC, was studied by the use of non-invasive and micro analytical techniques. EDXRF, Micro-EDXRF, SEM-EDS and Optical Microscopy were used to determine the alloy composition and to identify the different thermo mechanical operations applied in the production

A collection of 35 metallic artefacts comprising various typologies, some of which can be attributed to the Bronze Age and others to later periods, were studied to provide detailed information on elemental composition, manufacturing techniques and preservation state. Elemental analysis by micro-EDXRF and SEM–EDS was performed to investigate the use of different alloys and to study the presence of microstructural heterogeneities, as inclusions. X-ray radiography, optical microscopy and SEM–EDS were used to investigate manufacturing techniques and degradation features. Results showed that most of the artefacts were produced in a binary bronze alloy (Cu–Sn) with 10–15 wt% Sn and a low concentration of impurities. Other artefacts were produced in copper or in brass, the latest with varying contents of Zn, Sn and Pb. A variety of inclusions in the metal matrices were also found, some related to specific types of alloys, as (Cu–Ni)S 2 in coppers, or ZnS in brasses. Microstructural observations revealed that the majority of the artefacts were subjected to cycles of thermomechanical processing after casting, being evident that among some artefacts different parts were subjected to distinct treatments. The radiographic images revealed structural heterogeneities related to local corrosion processes and fissures that seem to have developed in wear-tension zones, as in the handle of some daggers. Radiographic images were also useful to detect the use of different materials in one particular brass artefact, revealing the presence of a possible Cu–Sn solder.

Micro X-ray fluorescence (micro-XRF) analysis and neutron imaging techniques, namely 2D radiography and 3D tomography, have been applied for the study of four metal axes from the Early/Middle Bronze Age in Western Iberia, a period characterized by a metallurgical change in the use of copper to bronze. Micro-XRF analysis has shown that one of the axes was produced in copper with some arsenic while the other three were produced in a copper-tin alloy (bronze) with variable tin contents and some arsenic and lead. Neutron radiography and tomography were applied to study internal heterogeneities of the axes in a non-invasiveway since the specificities of neutron interaction with matter allow a suitable penetration of these relatively thick copper-based objects when compared to the use of a conventional X-ray radiography. Neutron imaging allowed the visualization of internal fissures and pores and the evaluation of their distribution, size and shape. Relevant information for the reconstruction of ancient manufacturing techniques was gathered, revealing that one ax was produced with the mold in an angle of ≈25°, probably to facilitate gas escape during metal pouring. Also, information regarding physical weaknesses of the axes was collected, providing relevant data for their conservation.
Novelty statement: The present paper combines the use of micro-XRF and neutron imaging techniques, namely (2D) radiography and (3D) tomography for the study of prehistoric metal axes. The XRF spectra allowed identifying major and minor elements present in the alloys, inferring on the absence of elements that could become radioactive for a long period of time after irradiation with neutrons. The specificities of neutron interaction with matter allowed a suitable penetration of these relatively thick copper-based objects when compared to the use of a conventional X-ray radiography.
The combination of these non-destructive techniques allowed the evaluation of the metal composition and the internal structure of the axes. Micro-XRF allowed the distinction among copper and bronze axes, and provided data about the composition of early bronzes for which data is scarce. The neutron imaging study allowed for the first timethe visualization of internal heterogeneities in early bronze axes, namely pores and large voids, providing relevant information for the reconstruction of ancient manufacturing techniques and raising pertinent information regarding physical weaknesses of these types of objects.

A collection of 54 bronze artefacts recovered from the inland settlement of Castro dos Ratinhos (Portugal) and belonging mainly to the 9th–8th centuries BC, was studied by the use of non-invasive and micro analytical techniques. EDXRF, Micro-EDXRF, SEM-EDS and Optical Microscopy were used to determine the alloy composition and to identify the different thermo mechanical operations applied in the production of the artefacts. Results show that the collection is entirely composed of good quality binary bronzes (with an average tin content of 10.1 ± 2.5%). Alloys with higher tin contents were kept in as-cast condition and used in the making of ornaments, while tools were often finished with forging and annealing operations. Despite the existence of some Orientalising features in the Castro dos Ratinhos, e.g. rectangular habitat structures, wheel-turned ware and amphorae, the exclusive use of binary alloys with a narrow range of tin content seems to be associated with an indigenous metallurgical tradition inherited from the Late Bronze Age. This may indicate that the Phoenician interaction within the inland indigenous communities was a slow and selective process, probably dependant on the social-economic and cultural development of local communities.

A collection of 54 bronze artefacts recovered from the inland settlement of Castro dos Ratinhos (Portugal) and belonging mainly to the 9th–8th centuries BC, was studied by the use of non-invasive and micro analytical techniques. EDXRF, Micro-EDXRF, SEM-EDS and Optical Microscopy were used to determine the alloy composition and to identify the different thermo mechanical operations applied in the production

A combination of analytical techniques capable of elemental and microstructural characterisation was used for the identification of ancient gilding technology and bronze metallurgy. EDXRF, micro-EDXRF, SEM-EDS analysis and metallographic examinations were applied in the study of artefacts dating to the end of the second millennium BC from Crasto de São Romão in Central Portugal. Results report to the finding of an exceptional gilded copper nail among bronze artefacts with 9 wt.% to15 wt.% tin and minute other metallic impurities. Additionally, analysis of a crucible fragment points out for bronze production at the archaeological site. EDXRF and micro-EDXRF analysis made on the copper nail showed that it was gilded only on the front side of the head, and that the gold layer has been lost in the most exposed areas. SEM-EDS analysis showed that the gold layer has 5–8 µm in thickness and is covered with a thick corrosion layer. The gilding technique is discussed based on the gold layer composition and gold/copper substrate interface. So far, this object seems to be the first diffusion gilded artefact identified in the Portuguese territory dated to Late Bronze Age.

The knowledge of our pre-history and ancient metal artefacts production methods can only be deeply investigated through the multidisciplinary approaches involving different analytical techniques including microscopy techniques. The present study concerns the elemental and microstructural characterization of pre-historic bronze artefacts from the Northwestern Iberia Peninsula. During Bronze Age an increment of metal artefacts production and its typological diversification is observed related to the development of metallurgical technology. Several artefacts have been found during recent excavations at the Bronze Age settlement of Fraga dos Corvos (Macedo de Cavaleiros, Portugal). The analysis of metallurgical remains points out to the existence of local metallurgical activities. Five bronze artefacts previously analysed by micro-EDXRF, an Acebuchal fibula fragment, two pendants and a riveted sheet (probably a fragment of a vessel or cauldron) with average concentration values of 10±1.1% Sn and ~2±0.5% Pb and a droplet (?) with ~5% Sn and ~4% Pb, were selected for optical microscopy (OM) and SEM-EDS analysis.Microscopy observations showed to be very important for the comprehension of pre-historic bronze metallurgy, allowing the identification of different phases, inclusions and thermomechanical processes applied during artefacts production. The fibula and the pendants show an equiaxed and twinned microstructure with slip bands (Figure 1 (a) and (c)). The characteristics observed are related to recrystallized and plastically deformed α-Cu structures. These features indicate that the artefacts were hammered and annealed (thermomechanical cycling), ending with a hammering operation. The pendants only exhibit slip bands near the surface, probably resulting from a finishing operation. Lead and Cu-S inclusions are frequently observed. The riveted sheet has an annealed microstructure with large α-Cu grains, undissolved (α+δ) eutectoid and few annealing twins. Elongated Cu-S inclusions, lead globules and pores were identified by SEM-EDS (Figure 1 (a)). Its microstructure indicates that shaping was obtained by just one or few thermomechanical cycles. The droplet presents a coarse and cored dendritic structure (Figure 1 (b)). Rounded Cu-S inclusions, lead globules and pores were also observed. Those are characteristics of a slow cooled as-cast alloy. Due to its low Sn content the (α+δ) eutectoid is absent. As a final note, microscopy techniques allowed establishing the manufacture processes involved in bronze metallurgy and to conclude that different thermomechanical processes were applied according to the typology of the artefact.Financial support received from the Portuguese Science and Technology foundation under the EarlyMetal project PTDC/HIS-ARQ/110442/2008 and the grants SFRH/BPD/73245/2010 (EF) and SFRH/BD/72369/2010 (EL). Financial support of CENIMAT/I3N through the Strategic Project LA25/2011-2012 (PEst-C/CTM/LA0025/2011) is gratefully acknowledged.

... The obtained results also indicate that the yellow silver stain produced by the workshop of Ricardo Leone is richer in Cu, with ... Veritá, Composition, structure et mécanisme de détérioration des grisailles, Grisaille, Jaune d&amp;#x27;argent, Sanguine, Email et Peinture à Froid, Dossier de la ...

"Middle Bronze Age was a transition period in Iberia, characterised by the emergence of bronzes after more than a millennium of a conservative metallurgy of copper with arsenic. Despite its importance there are no relevant studies on MBA metallurgy in Southwestern Iberia due to the absence, until recently, of known settlements and the scarcity of metals. However, recent archaeological excavations have brought to light important finds dated to the SW Iberian Bronze Age such as new burial monuments
and open settlements. About 50 artefacts from hypogea, cists and domestic contexts (pits) from Torre Velha 3 (Serpa) and Monte da Cabida 3 (Évora) were analysed by micro-EDXRF, reflected light microscopy, SEMeEDS and Vickers microhardness testing. Radiocarbon dating of their archaeological contexts established a chronology of w1900e1300 cal BC. Despite presenting different burial practices both sites share the almost exclusive use of arsenical coppers (4.1
1.0 and 4.2
1.5 wt.% As, respectively).
However, few awls and a dagger from Torre Velha 3 are among the earliest evidence of bronze in SW Iberia, being dated to the second quarter of the 2nd Millennium BC. These bronzes are similar
(9.6
1.2 wt.% Sn) to LBA alloys suggesting trade with a region with a developed bronze metallurgy. The emergence of bronze in SW Iberia during the first half of the 2nd Millennium BC points to an earlier introduction or a more rapid expansion than initially assumed. Nevertheless, these arsenical coppers and bronzes display a similar manufacture involving hammering and annealing cycles. A final hammering increased the hardness, which could be higher for bronzes. Arsenical coppers display variable operational
conditions often with poorer thermomechanical work as expected from a prehistoric technology. A bronze dagger with silver rivets evidences the prestige value of early bronzes to MBA communities.
Similarly, an arsenical copper dagger with silver coloured rivets shows the ability of MBA metallurgists to replicate prestige objects with indigenous knowledge."

Metals and metallurgical remains from Outeiro do Circo were subjected to elemental and microstructural characterization. Radiocarbon dating of contexts established a chronology of last quarter of the II Millennium BC. A crucible was associated with gold production, while bronze nodules were related with bronze metallurgy.
A casting jet evidenced the pouring of a bronze alloy with similar composition to the remaining metallic artefacts, with the exception of an item, which reduced tin content probably is due to the use of scrap. The manufacture involved hammering and annealing operations. The analysed materials are in agreement with the
coeval metallurgy from southern Portugal, being characterized by binary bronzes with suitable contents of tin.

The Full Bronze Age artefacts from Torre Velha 3 were recovered in pits and funerary hipogea. If in the first
case several objects came from secondary contexts, some of them even collected in Late Antiquity pits, in
the second all artefacts are ascribed to funerary practices dated from the second and third quarter of the II
Millenium BC. These metallic artefacts from Torre Velha 3 typify a metallurgy of arsenical coppers with the
exception of few bronze artefacts that constitute the early evidence of this alloy in the Southwestern Iberia.
Composition of these bronzes suggests imports from another region with a more developed metallurgy, while
a bronze dagger with silver rivets evidences the prestige associated to those early bronzes. Manufacture of
arsenical coppers and bronzes usually include hammering and annealing.

Metals and metallurgical remains from Outeiro do Circo were subjected to elemental and microstructural
characterization. Radiocarbon dating of contexts established a chronology of last quarter of the II Millennium
BC. A crucible was associated with gold production, while bronze nodules were related with bronze metallurgy.
A casting jet evidenced the pouring of a bronze alloy with similar composition to the remaining metallic
artefacts, with the exception of an item, which reduced tin content probably is due to the use of scrap. The
manufacture involved hammering and annealing operations. The analysed materials are in agreement with the
coeval metallurgy from southern Portugal, being characterized by binary bronzes with suitable contents of tin.