Achaeometrical Research in Hungary II., 1988

ANALYSES - METALS - Géza SZABÓ: Evaluation of late Bronze Age Carpathian tinbronzes based on the alloying content

phase at perfectly identical parameters, in the same space, with the same focal length. When the surface was studied, the fragment of needle manufactured of a bronze pin with about 3 per cent of tin content, showed nearly 20 per cent i.e. about six times higher than the actual value of tin content (Figure 4). In the case of wire coil fragment, the surface segregation of tin was lower than with the needle, but the measured values indicated many times higher tin content than the actual value. So the studies justified the microscope observations concerning the tin-rich surface unambiguously. At the same time it means that the results of microspektrum analyses aimed at the surface or at near-surface layers of archaeological finds, particularly of annealed objects, should be taken with reservation (Figure 5-8). The impurities observed in the studied archaeological finds as Fe. Zn. As. Pb. Sb. Ni in quantities of several tenths of a per cent and the results of analyses of plate-backed fibula (SZABÓ: 1993 No. 87) show unambiguously the sulphide origin of the basic material used. Higher concentration of Sb occurred (in a per cent order of magnitude) only in the case of a sickle (SZABÓ: 1993 No. 47). and neither this nor the unusually high. 1.23 per cent nickel content is typical for the other appliances therefore it can be rather regarded as casual.(MACLEAN: 1993; MACLEAN-MCDONNELL: 1996) Presumably a fragment recycled for the casting of sickle had a higher antimony content (Figure 4). Lead is mostly present also in an order of magnitude of tenth per cents, but. as it can be seen also in microscopic pictures, it appears in form of small bluish-grey stains separated from the texture of the alloy. Data measured inside a twinned crystallite of a wire spiral fragment clearly show that there is no dissolved lead in the alpha-phase grains. In case of annealed objects the small quantity of unsolved lead migrates, sometimes completely, up to the surface, as e.g. in the case of plate-backed fibula, where it can be observed in a concentration of 25.25 per cent (Figure 4) In other cases the enrichment of lead reaches a factor of 15 (SZABÓ: 1993 No. 77) or even nearly 100 (SZABÓ: 1993 No. 130; Figure 4). As a conclusion, this means that the data from the microspektrum analyses aimed at the archaeological study of surface and near-surface layers must be treated with reservations due to lead segregation on the surface - similarly to the tin segregation -. particularly in the case of annealed articles. In the investigated objects the iron is present mostly in an order of magnitude of tenth of per cent. too. but some enrichment of the iron on the surface of annealed bronzes can be observed.(PAKSY: 1989; SZABÓ: 1993 No. 70.130; Figure 4). Larger segregation of iron, about 6 per cent, can be measured only in the single case of plate-backed fibula.(SZABÓ: 1993 No. 87) In the analyses of texture the plano-convex ingots formed a particular group with their higher iron content of per cent magnitude (SZABÓ: 1993 No. 174.177-178.181.184-186). On the XRF patterns of these articles the distinct iron peaks showing an iron content of about 4 per cent can be clearly identified, and the curve, completely smooth in other regions, clearly shows the extraordinarily low tin content present in quantities not higher than tenths of per cent. The alloying metal content of the analysed objects, in accordance with the microscopic picture of polished surfaces, showed a low tin content in every case, along with other components present in a ratio of tenths of percent, and so regarded as impurities. Only the ingots show a different composition: their iron content is higher, about 4 per cent, while their tin content is quite low (Figure 4-7). 161