The Occurrence of Metallic Iron in Ancient Copper

• Published in: Journal of field archaeology 1975-01, Vol.2 (3), p.251-266
• Main Authors: Cooke, Strathmore R.B., Aschenbrenner, Stanley
• Format: Article
• Language: English
• Subjects: Alloys; Copper; Ferrous minerals; Furnaces; Iron; Iron alloys; Iron oxides; Slag; Smelting; Specimens; Technical Studies
• ISSN: 0093-4690; 2042-4582
• DOI: 10.1179/009346975791491015

Of the many thousands of chemical or spectrochemical analyses of ancient copper, principally from central and northern Europe, and available in the literature, only a few report iron in excess of 1% and, in general, of these the iron occurs in Iron Age metal. On the other hand, some recent articles report much higher iron, these data being supplemented by our own investigations. These high-iron coppers are from Sardinia, Greece, Israel, Egypt, and India, and range in date from the Chalcolithic and Early Bronze Age through the Iron Age. Of 61 copper specimens found at Nichoria, a recently excavated site in the sw Peloponnese, 11 were found to be ferromagnetic, and ranged in age from Early Bronze Age to Byzantine. In a number of specimens, which have been examined spectrochemically and metallographically, the magnetic response is closely proportional to the total iron in the sample. Although Iron Age copper that contains appreciable iron can be explained by accidental addition of the impurity, no such explanation is applicable to the much earlier high-iron copper. It is therefore proposed that the iron was introduced as a result of simultaneous reduction of iron oxides in the furnace burden to solid metallic iron during the copper smelting operation. This phenomenon may have been more widespread than is realized. It is pointed out that in the smelting of low-sulfur copper ores, the iron content of copper prills in an unweathered slag can be used to determine the minimum temperature reached in such an operation and, under favorable conditions, perhaps the maximum temperature reached, thus furnishing a clue to the currently moot question of the temperature attained in an ancient charcoal-fueled smelting furnace.