Bronze archaeological

Climent-Font, A., Demortier, G., Palacio, C., et al. (1998). Characterisation of archaeological bronzes using PIXE, PIGE, RBS and AES spectrometries. Nuclear Instruments and Methods in Physics Research B 134 229-236. 

Segal, I., Kloner, A., and Brenner, I. B. (1994). Multielement analysis of archaeological bronze objects using inductively coupled plasma-atomic emission spectrometry -aspects of sample preparation and spectral-line selection. Journal of Analytical Atomic Spectrometry 9 737-744. 

While thousands of analyses of archaeological bronzes have been reported in the literature, the basis for comparing them, especially those from different laboratories, is shaky. A round-robin project of chemical analyses was attempted to improve the situation. Two ancient bronze objects were milled to a fine powder, sieved, and mixed to a homogeneous mass. Samples of 500 mg each drawn randomly from this mass were circulated, and results were returned from 21 laboratories. Forty-eight elements were analyzed some laboratories did only one element, some did as many as 42. The coefficient of variance (or relative standard deviation) ranges from 4% for Cu up to over 200% for some trace elements. The results are tabulated, and methods are suggested to narrow the spread of results in the next run of this program. 

Table II shows, in some detail, the complexity and variability of the population involved in this study (laboratories analyzing archaeological materials) and of the reporting procedures. Even the elements analyzed by each laboratory are not completely clear. For example, laboratory 02 reported Cr in trace amounts (0.0001-0.001% ) in samples 1 and 2 but gave no report for sample 3 (the space is blank). Thus, we assume that they did not look for Cr in sample 3 although it seems equally likely that they looked for it and it was not present. The proper use of the term not detected, the consistent reporting of detection limits (done by few laboratories), and the choice of elements to be determined in archaeological bronzes are all open questions.

Known samples with stated values of the elements of interest should be circulated, along with the unknowns, for calibrating the methods used in the various laboratories. Standards of known composition should also be included with the unknowns. It is possible that standard archaeological bronzes should be synthesized for this program and for future circulation. Also, the statistical basis of the program should be reassessed and a new statistical design drawn up so that data collection and analysis can be simplified. Since many archaeologists and museums use the services of commercial laboratories, samples should be circulated to these laboratories for paid analysis. 

Although the earliest known bronzes are arsenical bronzes from the Levant and Mesopotamia, most archaeological bronze is tin bronze. There are copper-tin sulfide ores that might have been accidentally, then intentionaUy, used, but most tin is available in cassiterite or tin oxide, which is not usuaUy associated with copper deposits and would have to be deliberately sought for its utiUty for making bronze. 

It is possible to produce alloys from ores. Archaeological bronze is an alloy of copper and tin and the alloys were made by mixing tin ore, (cassiterite, Sn02) with pure copper, covering the mixture with a layer of charcoal and heating to approximately 800°C. Liquid alloy was tapped from the furnace. 

Some of the non-ferrous metals and alloys have already been mentioned such as copper and brass. Archaeological bronze is an alloy of copper and tin. The composition of these alloys ranges typically from 3% to 14% tin together with trace impurities such as lead and iron, depending on the chemical content of the original ores. Alloys with atin content, up to 6%, were capable of being cast and subsequently hammered into their final shape. This is due to the tin being soluble in the copper crystal structure, which allows the alloy to be deformed at room temperature. 

Figure 5.35 is an image of an archaeological specimen comprising a small fragment of a Urartian bronze belt of about the 8th 7th centuries BC. 

Cherry, J. F. and A. B. Knapp (1991), Quantitative provenance studies and Bronze Age trade in the Mediterranean Some preliminary reflections, in Gale, N. H. (ed.), Studies in Mediterranean Archaeology, Astroms, Jonsered, Vol. 40, pp. 92-111. 

Clow, P. (1982), The Prevention of Bronze Disease in Archaeological Specimens, thesis, Portsmouth Polytechnic, Portsmouth. 

Merkel, J. F. (1990), Experimental reconstruction of Bronze Age copper smelting based on archaeological evidence from Timna, in Rothenberg, B. (ed.), The Ancient Metallurgy of Copper, International Association of Meteorology and Atmospheric Sciences, London, pp. 78-122. 

Sandu, I., F. Diaconescu, I. G. Sandu, A. Alexandru, A. Sandu, and V. Andrei (2006), The authentication of old bronze coins and the structure of the archaeological patina, Analele Universitatii "Dunarea de Jos" din Galati, Fascicula IX Metalurgie si Stiinta Materialelor, 24(1), 38-48. 

A second application of DI-MS was in the analysis of archaeological adhesive of a blackish amorphous residue present on the chape of a bronze sword, discovered in a tomb from the Iron Age (ca. 800 700 BC) at the archaeological site of Argancy (Moselle, France). In the mass spectrum (Figure 3.13) the ion fragment at mlz 189, which is characteristic of triterpenoid compounds, is evident and represents the base peak. 

Copley, M. S, Berstan, R., Dudd, S. N., Straker, V., Payne, S. and Evershed, R. P. (2005b) Dairying in antiquity. II. Evidence from absorbed lipid residues dating to the British Bronze Age. Journal of Archaeological Science 32, 505 521. 

Shortland, A., Rogers, N. and Eremin, K. (2007). Trace element discriminants between Egyptian and Mesopotamian Late Bronze Age glasses. Journal of Archaeological Science 34 781-789. 

Hughes, M.J., Northover, J.P. and Staniaszek, B.E.P. (1982). Problems in the analysis of leaded bronze alloys in ancient artefacts. Oxford Journal of Archaeology 1 359-363. 

Connan, J., Nissenbaum, A. and Dessort, D. (1992). Molecular archaeology export of Dead Sea asphalt to Canaan and Egypt in the Chalcolithic-Early Bronze Age (4th 3rd Millennium BC). Geochimica et Cosmochimica Acta 56 2743-2759. 

Silver items, however, are also relatively rare in the archaeological record. The most common metal found is either copper, usually alloyed with either tin (bronze) or, in the later periods, zinc (brass), or iron. The latter contains very little lead and, because of severe corrosion problems, its survival rate is often low (but see Degryse et al., 2007). Fortunately, copper can also be characterized from its lead isotope signature, since the primary ore of copper is chalcopyrite (CuFeS2), which often co-occurs with galena (PbS) and sphalerite (ZnS). Even if the ore used is a secondary mineral formed by the oxidation of the primary deposit, the copper smelted from such a deposit would normally be expected to... 

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