Study of Archaeometallurgical Slag and Metal

Abstract

The 'Most Ancient' Slags Ancient slag from non-ferrous metallurgy has mostly been divided into two groups based on technological grounds: smelting slags and crucible slags (melting/refining/ casting slags). Samples analyzed from the former have been mainly from sites dating into the (Late) Bronze Age, Iron Age or even later periods and were collected from large slag heaps, which indicated a mass production of metal. Crucible slags, on the other hand, were classified as waste products from the processing of non-ferrous metals e.g., by remelting or alloying. They acquired their name from the small crucibles in which these processes were carried out. Crucible slag has been analyzed, e.g., from Late Bronze Age tin-bronze casting workshops in Kition (Cyprus) (Zwicker et al. 1985), Nichoria (Cooke and Nielsen 1978), Isthmia (Rostoker et al. 1983), and Olympia and Athens of the classical period (Zwicker 1984). Cooke and Nielsen (1978) and later Craddock and Freestone (1988) worked out criteria for the definition of crucible slag based on suggestions for the differentiation between smelting and crucible slag (Tylecote 1976). The remains of the pottery crucibles still adhering to the slag are one unmistakable attribute. The slag is often attached to the rim of the crucible and shows transitions to the pottery (Hauptmann et al. 1993, Klein and Hauptmann 1999). Chemically, crucible slags are alkali-aluminum silicates, which develop by reactions between metal and oxide melts with crucible material, Fe-contents in the copper, charcoal ash and silica-rich fluxes. Their SiO 2 + Al 2 O 3 /FeO + MnO ratio is high. Cu and/or Cu 2 O concentrations are higher than those of the smelting slags. Crucible slags are heterogeneous, largely glassy and porous, while smelting slags are well crystallized and show only a few large gas bubbles. Fayalite appears typically in smelting slag but not necessarily in crucible slag, while the latter contains higher-valent oxides, e.g., delafossite. This definition becomes less clear-cut when one looks at the slag from the beginnings of extractive metallurgy. Several studies demonstrate that at least up to the beginning of the Early Bronze Age I, pottery crucibles were used for most of the metallurgical processes (Maggetti 1990; Palmieri et al. 1993; Hauptmann et al. 1993; Müller-Karpe 1994; Rehren 1997b, Craddock 2002). For a long time, this fact hindered the precise understanding of the initial stages of metallurgy, as can be shown by the example of the slag from Çatal Hüyük (Anatolia), an early Neolithic settlement from the middle of the 7 th millennium BCE. The minute slag granules were published by Neuninger et al. (1964). The unusually early date and the rather lim