Temperature estimates of historical Pb-Ag smelting slags: A multi-methodological approach

The process temperature is a key parameter for the reconstruction of historic smelting operations since it can provide valuable information on the technological state-of-the-art as well as on intrinsically related aspects such as the type and availability of fuel (e.g. charcoal, wood) and metallurgical know-how. Slag compositions in leadsilver metallurgy can show a wide variation due to the utilisation of variable raw materials and possible addition of fluxes, but also since Pb oxide can be a major component, affecting the thermal behaviour and viscosity of the slag melt. This study presents results for liquidus temperatures determined by a range of different data-based and experimental techniques - phase diagrams, thermometry calculations, differential thermal analysisthermogravimetry (DTA-TG) and hot stage microscopy (HSM) - applied to a suite of slags broadly representative of the compositional and mineralogical spectrum of metallurgical remains of lead-silver smelting. We propose suitable applications of the different techniques and provide generalised archaeometallurgical implications for the investigated slag types.