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The work reported in this article forms the basis for an extended study of arsenic bronze. The ease with which a copper-arsenic alloy could be prepared by fusing copper metal with arsenopyrite has been shown; conditions can be readily adjusted to yield alloys with compositions equivalent to those made in antiquity. While iron-metal prills were found in the fused crucible remains, it is probable that such metallic iron will only be observed in ancient crucible sherds when full vitrification has taken place, otherwise the iron will weather over time to oxide.
INTRODUCTION
Ancient arsenical copper-bronze alloys are particularly interesting to archaeologists, as their sources and modes of preparation and/or selection reflect the skills available to ancient societies as well as the distribution of the people with these skills. If copper were reduced from an orestuff composed of either copper ore and arsenic ore, such as arsenopyrite (FeAsS), or a copper ore containing arsenic, then a high-arsenic copper (up to five percent arsenic or more) can be obtained by direct smelting, as in the smelting of arsenical coppers in the South Americas. However, if lead ores are present in the orestuff, the removal of the lead results in the virtual elimination of arsenic in the copper.1
A copper-lead mixed ore source requires a refining stage during the smelting operations to reduce the lead content if a reasonably pure copper metal is required. A well-established and ancient process for achieving this is through oxidizing fire refiningin effect, a cupellation.2 An air blast is played over a bath of molten copper, oxidizing the lead to molten litharge (PbO), which is blown off the melt and absorbed in the furnace bed. During this procedure, any arsenic that is present is rapidly oxidized and released as fume (As^sub 2^O^sub 3^). The process is particularly efficient in oxidizing the arsenic since copper oxide is formed to some extent during the operation, and this has a powerful oxidizing effect. After the lead and other contaminants, such as arsenic, iron, and zinc, have been removed, charcoal is added to the melt to reduce any copper oxide to copper metal. By this means, if arsenic is present in the original ore its final content is reduced to under 1% in the final copper.3