Reconstruction of 16th–17th Century Lead Smelting Processes on the Basis of Slag Properties: A Case Study from Sławków, Poland

Abstract

The study focuses on the reconstruction of the technological process in the 16th–17th century lead smelter in Sławków based on chemical and petrographic analyzes of slags. There are three main types of material at the landfill: glassy, crystalline, and weathered. Glassy slags are made of amorphous phase in which crystals of pyroxene, willemite, olivine, wüstite, and lead oxide appear. Crystalline slags are composed of wollastonite, rankinite, melilite, anorthite, quartz, and Fe oxides. Weathered slags have a composition similar to glassy slags, but they also contain secondary phases: anglesite and cerussite. Chemical analyzes confirmed that the smelter used sulphide ores, which were roasted, and the main addition to the charge was quartz sand. The smelting process took place in a brick-built furnace, under reducing conditions, with varied oxygen fugacity ranging from WM to MH buffer. The slag characteristics show a knowledge of the workers in the field of smelting methods. The addition of SiO2 allowed for the binding of elements that could contaminate the obtained lead, and at the same time, the low melting point of the material (1150 °C) and the melt viscosity (logη = 1.34 for 1150 °C) was maintained, enabling the effective separation of liquid lead.

Reconstruction of Copper Smelting Technology Based on 18–20th-Century Slag Remains from the Old Copper Basin, Poland

“…Arkose sandstones could also be a source of K 2 O in slags, which is generally higher than in ores. The addition of sand was previously observed in numerous examples of historical metal smelting, e.g., in Poland [2], the Czech Republic [31], or South Africa [32]. In the case of the Old Copper Basin slags, the addition of sandstone flux would carry an unfavorable increase in melt viscosity (which is observed in slags and is discussed further).…”

“…In these situations, spinels, mainly magnetite, are often present [13]. Oxygen fluctuations could be pointed out by the presence of various iron oxides, e.g., magnetite, hematite, and wüstite [2].…”

“…0.50) indicate a low efficiency of metal separation between silicate and metallic phases. Low viscosity values in historical slags often result from a high concentration of oxides not included in the equation, e.g., PbO and ZnO, for which specific corrections were suggested [1,2,14]. However, because only insignificant amounts of other oxides are found within the analysed set of slags (Table 1), and oxides included in Bachmann's calculations constitute 96-98.5 wt%, we did not include the aforementioned corrections.…”

“…Pyrometallurgical slags are common metal smelting remains that record details of their origin in the matter of geochemical and mineralogical imprints pointing to the technological process of their production [1,2] or isotopic composition suggesting the metal deposit from which the ore was mined to be used in a given process [3,4]. Because historical metal smelting technological processes are rarely described in written sources, it is essential to reconstruct this technology based on accessible remains for the recognition of changing technology.…”

“…These include the recognition of various metal smelting technologies, including Cu [13] Pb-Ag [1,14], Ag [10], and Zn [15]. After a three-year hiatus, reconstructions of the smelting Minerals 2021, 11, 926 2 of 21 conditions have recently become acknowledged again [2,16,17]. Still, only a few papers on the reconstruction of historical base metal smelting from Poland have been published in the past, and there are no data regarding the important copper mining and smelting centre, which is the Old Copper Basin.…”