The remains of a mediaeval settlement were found at the Gutenwerd archaeological site. In addition to other archaeological remains, slag remains were also found, showing that iron alloys was also produced and processed in the settlement. As part of Master thesis, we analysed samples of eight slags. We tried to find out whether the slags were produced in the process of extractive metallurgy, i.e. during the reduction of iron ores, or whether they were produced in the forge furnace during the processing of the semi-finished metal product. We prepared two samples for each slag. The first sample was used to determine the mineralogical composition by X-ray powder diffractometry. The second sample was prepared for scanning electron microscopy (SEM) to examine the microstructure of the slags and analyse their chemical composition using energy dispersive spectroscopy. Based on the results of the analyses, the slag samples were divided into two groups. The first group includes slags that were formed in the smelting furnace and consist mainly of fajalite and wüstite. The slags from the smelting furnace were further subdivided according to the type of furnace in which they were created. Forging slags have a more diverse composition due to the use of different fluxes in the forging process. The presence of potassium and calcium indicates that the ash from the burnt charcoal was trapped in the slag, and the presence of quartz indicates the use of silica sand in the forging process. Metallic iron trapped in the slag was also observed in some samples. This indicates slightly worse process efficiencies.
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