M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)
Analysis - GEGUS Ernő: Investigation of archaeological bronze and silver findings by using various emission spectroscopic methods
GEGUS Ernő* INVESTIGATION OF ARCHAEOLOGICAL BRONZE AND SILVER FINDINGS BY USING VARIOUS EMISSION SPECTROSCOPIC METHODS 1 Abstract — A spectrochemical method is described for determining the elemental composition of archaeological alloys, mainly for trace element analysis. Solution of a small mass sample in a concentration of 50 mgjmL is introduced into a spark discharge or stabilized d.c. arc source, and the UV range is recorded on a plane-grating spectrograph. Calibrating with synthetic reference solution samples enables a "quasi-absolute" analysis to be performed. Precious findings are investigated by using a "quasi-nondestructive" laser-micro-spectral analysis method. In many cases, for determining quantitative chemical composition, suitably selected reference samples are analysed by means of the "quasi-absolute" analysis method in solution, and the use of both methods will be combined. 1. Introduction The composition of archaeological alloys is quite different from that of the alloys used today; the standard sample problems are, therefore , more difficult. Spectral analysis in solution is a "quasiab solute" analytical method in which the calibration can be performed by using synthetic standard samples of calculated composition. The multi-element spectral analysis method of solution-micro-samples has been elaborated by introducing aerosols into a high-voltage spark source [1 ]. A micro-sampling method for representative analysis of non-homogeneous coins was recommended by Szonntagh [2]. It is not always possible to take even a micro-sample, in view of the high value of several findings, e. g. archaeological coins or jewels. Nondestructive analysis methods (X—ray fluorescence and emission spectrometry, etc.) are often used for serial determination but mainly for major components. A very simple multi-elemental "quasi-nondestructive" laser-microspectral analysis method has been elaborated and applied [3] for the semiquantitative determination of the composition of Roman bronze coins, also including trace elements. Based on homogeneity studies on cross-sections of selected coins [4], it has been stated that micro-plasmas, obtained from a 0.1—0.2 mm deep crater of about 0.1 mm in diameter, on the edge of the coin, gave characteristic results for the composition of the sample [5]. Similar investigations have been carried out on 3rd century Antoniniani silver coins originating from various mints [6]. In consequence of the well-known blanching process, as well as the diffusion and corrosion in the soil [7, 8], the ratio of the main elements Ag/Cu in the surface layer and inside the coin could be different, but the trace element content and the ratio of these during laser investigation have been found characteristic. Furthermore, the original laser-micro-spectral analysis data (logarithmic-intensity values of spectral tines of trace elements) were processed by using pattern-recognition methods, and an efficient classification of the investigated samples was achieved without calculating the chemical composition of the samples [9,10]. * Research Group of Analytical Chemistry of the Hungarian Academy of Sciences H-8201 Veszprém, P.O.B. 158 1 Presented as a poster at the 24th Coll. Spectr. Inter., Garmisch-Partenkirchen, 1985 (unpublished)
