GENERAL — 56/262 — Old silver mining
The minerals mined in the Kuttenberg belts, primarily galena, sphalerite, and chalcopyrite, were characterised by a low silver content, making its smelting a rather challenging process. Work in the smelters was continuous. Furnaces with open spouts for easier handling of metal were used, or more often, those with closed spouts for better temperature regulation. This refinement process was described in great detail, for instance, in Agricola's illustrated work from 1556. The medieval process of silver extraction consisted of four stages. Almost every step had to be repeated several times to achieve the desired result. The raw material's structure and composition changed from the form of rocks and solidified slag to molten silver with lead impurities and finally to a solid "loaf" of pure silver. The primary goal was to remove unwanted impurities and reduce the ore's weight to a minimum. The final phase - silver refining through the addition of a specific amount of pure lead and the separation process (cupellation) - was known as far back as antiquity. Silver was melted with lead in a so-called cupellation bowl, where unwanted mixtures of other metals were separated through air oxidation.
TRIVIA
— Archaeometallurgical findings are a precarious source for determining the location and profitability of medieval silver mines. Most of the older mines are either abandoned for centuries or they were re-used and expanded over time, and much of the few remnants that can be found comes in the form of slag – a waste material that was often enriched with lead to make processing easier, could be recycled and was only 'kept' when in the worst quality, while purer ore could often be processed directly. Due to the significance of silver as the primary source of coins, such silver veins would be exploited right away, while within the slag that was found and analysed on medieval mining sites, a silver concentration of 1% was rarely exceeded. Historical texts, on the other hand, paint a drastically different picture. The 16th century mineralogist and metallurgist Agricola, for example, classifies ores containing less than 3% of silver as poor and undesirable, while the 10th century Yemen-based scholar al-Hamdānī even speaks of veins that contain anything from 0.8 up to 50% of silver. However, written records are sparse, especially for the oldest mining activities of the early Middle Ages, and those that do exist are often written both with a lack of scientific accuracy and a great element of sensationalism – not least to draw in new entrepreneurs to establish their own mining sites and thus help to boost another 'silver fever'.
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