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Ancient Technologies and Archaeological Materials
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University of Illinois at Urbana-Champaign
ATAM is a Division of the Illinois Transportation Archaeological Research Program
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MURLO SLAGS


Nine samples of slag from the sixth century B.C. Etruscan site at Murlo, Italy, were analyzed for microstructure and composition using light microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) to answer the following questions: Is the material copper smelting slag, or the product of early iron smelting? How efficient was the smelting process? Can information be gained about the temperature and atmosphere inside the smelting furnace? How do these slag samples compare with previously analyzed examples that derived from a different location at the same site? Because the slags revealed different phases (both glassy and crystalline, with some ceramic furnace remnants attached) both to the naked eye and under a metallurgical microscope, several samples from each slag piece were prepared.



Slag sample 3
 The combined results reveal a high iron-content (average over 90% Fe) slag from copper smelting, similar in composition to slags already analyzed from other furnace areas at the same site. The slag is primarily three types of fayalite, or iron silicate (Fe2SiO4 or (FeMg)2SiO4 or (FeMn)2SiO4 and some wuestite (FeO). Dendritic structure was apparent, especially in fayalite of sample # 3.

Quartz (SiO2) or opal/cristobalite (SiO2) was present in a few localized areas, probably a result of an added flux or as inclusions in the clay furnace lining rather than as a direct result of smelting copper.




Copper spot in sample 9
 The greenish spots in sample # 9 proved to be copper, but the total amount of copper present in all the samples was low, indicating an efficient smelting process. The temperature reached in the furnace must have been about 1200 o C since fayalitic phases form within a range of 1100 o C and 1177 o C.




Interface of slag and clay in sample 3
 The clay lining of the small oven/crucible (sample #3) used for smelting was characterized by EDS. It has a typical clay (alumino-silicate) composition of Si (a very large peak), Al, K with traces of Fe.

The EDS results on the slags were confirmed by X-ray fluorescence (XRF) analysis, conducted by Yan-Hong Zhang at the Illinois State Geological Survey. Sarin calculated the oxide weight percentages of the EDS data and found that the results matched very closely with those obtained by XRF.



Copyright 1999. University of Illinois at Urbana-Champaign.