A GLOBAL APPROACH TO THE PRODUCTION OF IRON IN ANCIENT GREECE

• G. D. Papadimitriou (Laboratory of Physical Metallurgy, School of Mining and Metallurgic Engineering National Technical University of Athens, 9 Iroon Polytechniou str., 157 80 Zografou, Greece)

Lumps, pieces of slag with hemispherical shape and furnace bottoms are very often digged out in excavations and are bearing witness of more or less important metallurgical activities in the field. In many cases, these metallurgical relics are easily recognized as remains of some metallurgical procedure related to iron, as -beside their usual hemispherical shape- they exhibit a more or less earthy appearance and a brownish colour, which is related to iron compounds.

Although this first step of recognition of the iron slags is an easy one, it is however very difficult to determine whether they are pertinent to the original process of metallurgical production of iron from the ore or are simply related to a metaworking process of fabrication, characteristic of a smith's forge.

In many cases the slags are remote from known ore deposits suggesting rather metalworking activities, but their important quantity justifies better the opposite hypothesis of an extractive process, despite the absence of close ore resources.

The problem of the exact identification of iron slags is difficult to resolve not only by archaeologists, but even by experimented metallurgists. At first, the distinction between metallurgical and forging slags of iron is complicated by the fact that the residues of both activities have very similar appearance. Secondly, they have very similar chemical and mineralogical constitution. As a matter of fact, the production of iron in the antiquity is a solid state procedure comprising partial reduction of iron ores, so that the furnace slags consist of oxides and silicates, often in a semi fused condition. Almost the same compounds are produced during the refining and forming stage of a metalworking process, which is however a slightly oxidizing process.

Therefore, the distinction between metallurgical and metalworking slags is very subtle and requires detailed metallographic, chemical and mineralogical analysis. Furthermore it is necessary to fully understand and take into consideration the metallurgy of iron, from the ore to the final product, as it was practiced in antiquity.

In this perspective we try to present the ancient metallurgy of iron as a global approach, taking into consideration historical and archaeological data, as well as previous investigations on the subject. The works done in a metallurgical production furnace and in a refining or a smith's workshop are defined and described with reference to products and rejects. We try to show how these jobs were strictly limited by the technological possibilities of that period, so that no margins for innovations were left over a very long period of time.

In a second part we have proceeded to the examination of a number of iron residues using contemporary techniques (x-ray diffraction, scanning electron microscopy and micoanalysis) trying to clarify crucial points. Iron lumps, furnace bottoms from both metallurgical extraction and smithing actions are examined in detail. Also the slag inclusions of a considerable number of ancient irons and steels are studied using the same techniques.

In a final part the above results are discussed and explained, in a perspective to determine criteria, allowing to judge about the metallurgical processes responsible for each kind of slags and to explain the microstructure and constitution of metallic materials (iron and steel) associated to the relevant metallurgical processes.