Rapid cooling effects in Early Bronze Age copper smelting slags from Chrysokamino

M.G. Clinton, S. Martino, G.H. Myer, D.O. Terry, Jr. & P.P. Betancourt Aegean Archaeology 8 (2005-2006) [2009]: 21-30.

Abstract

During the Early Bronze Age, the promontory of Chrysokamino in the Mirabello Bay area of Crete housed a small copper smelting installation. Under the direction of Philip P. Betancourt, a team from Temple University excavated the site from 1996 to 1997. Slag from the smelting operations was abundantly present, up to sixty centimeters deep. Initial analyses of the slag suggested that the smelting operation, although relying upon simple technology, was nonetheless effective. With chimneys and artificial draft, the furnaces probably reached temperatures of up to 1230° C, sufficient to separate copper from its ores and produce slag. Utilizing petrographic thin section analysis, we offer new descriptions of Chrysokamino slags, including slag condensed inside chimneys and slag from furnaces. Our analysis of the furnace slag identifies several microscopic structures, such as plagioclase crystals, pyroxene crystals, and a glassy matrix with olivine. Olivine only forms at temperatures above 1200° C, so we confirm that the furnaces reached temperatures high enough to smelt copper. In addition, the form of the crystalline structures, which appear to be quench crystals, suggests that the slag cooled rapidly upon exposure to air; thus, we suggest that we have identified tapped slag. We differentiate the tapped slag from the chimney slag by illustrating the greater abundance of crystalline structures, especially pyroxene, and absence of olivine, which indicates that the chimney slag cooled at a lower temperature and more slowly. This new analysis confirms that the smelting process at Chrysokamino was both effective and efficient.