Roman leaded bronzes

Bronze was used by the Romans for the fabrication of objects of different siz.es and uses ranging from small tools to huge statues [17-20]. The three leaded bronze samples (hereafter 1 to 3) and the copper sample (used for comparison purposes) analyzed here were provided by the Museo della Civilta Romana (Rome). They date from the third century B.c. and were found in an excavation carried out in Carsbli (Italy) in 1908 [21]. 

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As examples, two related types of ancient objects have been analyzed, both of Roman origin a lead pipe, or fistula, and a series of leaded bronzes. Information about their surface chemical condition is essential, but, since their surfaces are highly heterogeneous, so is spatially resolved information. 

The Phoenicians were building water ducts and pipelines of clay, stone, or bronze about 1000 B.c. and the construction of long-distance water pipelines flourished in imperial Roman times. The water supply lines of Rome had a total length of about 450 km, and consisted mainly of open or covered water ducts. The Roman writer Vitruvius gives a fairly accurate description of the manufacture of lead pipes [8]. The pipes were above ground and were often laid beside the roadway or in ducts inside houses [9]. 

Lead, called by the Greeks molybdos, by the Latins plumbum, by reason of the wide occurrence of its ores and the readiness of its reduction, was known at a very early period. It was used by the Babylonians in the form of thin plates for engraving inscriptions, and by the Egyptians and other early civilized peoples for a variety of purposes. We have already noted its use by the Egyptians as a constituent of bronzes, a use which Pliny also records in Roman times. The Egyptians called lead the mother of metals, an idea which may have arisen from the frequent... 

Lead curse tablets from Roman Carthage contain variable amounts of very small metallic inclusions. Electron microprobe analysis confirmed these metallic inclusions were bronze, brass, and a Sn-Sb alloy. This was interpreted as possible evidence of lead metal recycling. Six samples were chosen to represent a range of tablets containing the minimum to the maximum number of inclusions. Thermal ionization mass spectrometry of the Pb isotopes in the curse tablets appear to define a mixing line, with the tablets containing the least number of inclusions plotting closest to the Tunisian lead ore isotope ratios. 

Tin [7440-31-3] is one of the world s most ancient metals. When and where it was discovered is uncertain, but evidence points to tin being used in 3200—3500 BC. Ancient bronze weapons and tools found in Ur contained 10—15 wt % tin. In 79 AD, Pliny described an alloy of tin and lead now commonly called solder (see Solders and brazing alloys). The Romans used tinned copper vessels, but tinned iron vessels did not appear until the fourteenth century in Bohemia. Tinned sheet for metal containers and tole (painted) ware made its appearance in England and Saxony about the middle of the seventeenth century. Although tinplate was not manufactured in the United States until the early nineteenth century, production increased rapidly and soon outstripped that in all other countries (1). 

The densities of many of the lead-containing coins are higher than the density of copper (8.93 g/cm3). However, bronze (Cu-Sn alloy) and brass (Cu-Zn alloy) both have densities below that of pure copper, and indeed, the measured densities of our coins reflect this fact. However, some of the cast coins have densities somewhat lower than expected from their chemical compositions. This low density is probably caused by interior porosity, which is rare in Roman Imperial coins (the hot striking of these coins would tend to close internal pores). The density of coin T-1600 is 7.79 g/cm3. This very low density is caused by extensive interior corrosion of the coin. In fact, the coin seems to have noticeably expanded because of corrosion along grain boundaries into the interior of the coin. 

By the time that the Romans came to Britain, iron and bronze were being used for weapons and tools copper for vessels and ornaments lead for pipes and coffins silver and bronze for coinage and gold, silver and tin for ornaments. A considerable number of Roman drinking vessels have been found made of pewter, which is an alloy of lead and tin. Even the Romans must have known something about lead poisoning as their superior quality pewter had a lower level of lead in the alloy 20% instead of the normal 50%. 

The earliest Roman bronzes that have come down to us date from the fifth century b.c. and contain tin about 7 per cent, and lead from 19 to 25 per cent. This was the alloy used for casting the large coin (8 to 11 oz) of the Republic, known as the As. These ternary alloys were continued in use as coinage until 20 b.c. but from that date until two centuries later lead is seldom found in Roman coins except as an accidental impurity. The lead was no doubt added partly to increase the fusibility of the alloy and also because of its cheapness as compared with copper and tin. Roman bronze statues often contain 6 to 12 per cent of lead. Gowland states that the Japanese were accustomed to add lead to bronze, not merely for cheapness and increased fluidity but also to enable the development, under suitable treatment, of a rich brown patina J. Pliny gives a tip to the house-wife. When bronzes are cleaned,... 

Among leaden articles belonging to the Roman period are pipes, coffins, cists, etc. The Romans also used articles of pewter (p. 211), at that time an alloy of lead and tin in the ratio of 1 to 4. Probably the two metals were deliberately mixed to produce the pewter, for the Romans were familiar with solder. It is possible, however, that pewter may have been produced in the first instance from a natural mixture of tin and lead ores, just as bronze resulted from a mixture of tin and copper ores (p. 91). Professor Louis has recorded such an occurrence m the Far East, where he found the Chinese smelting a natural mixture of lead and tin ores obtained by washing certain alluvials in the State of Patain in the northern part of the Malay Peninsula. 

To summarize the archaeological applications of lead isotope analysis, we note that despite the problems of ore body identification and metal recycling, it is becoming possible to build up the geographical details in the early history of metal making [28] for China [29] and for Bronze Age Europe, as well as later applications such as the mining of lead by the Romans in Germany [30]. 

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