9/26/2023 0 Comments Copper patina mirrorFurther minor elements included nickel, silver, tin, zinc, iron, and bismuth. The most important one is lead, with contents of up to 1% by weight, followed by arsenic and antimony, often up to 0.5% by weight. This explains why old copper samples contain larger amounts of oxygen (ranging from 400 to 4000 ppm by weight) and other metallic impurities. After this, oxygen became the agent that helped to reduce sulfur and other major and minor elements contained in the ore. In the mine of Falun (Sweden), for instance, lead and zinc sulfides were the main constituents. Often the copper ore was a minority component in an ore body. Well-known Fahlerz deposits were exploited until the 19th century in Schwaz (Austrian Tirol) and Neusohl (Slovakia), which belonged to the Austro-Hungarian Empire. They range from rather pure chalcopyrite (CuFeS 2) to the Fahlerz ore with high antimony and arsenic contents. These ores were rapidly exhausted in Europe, and ancient metallurgists had to learn to obtain the copper from a large variety of copper sulfide ores. In early times, native copper and copper extracted from oxide ores was obtained through a reduction with charcoal. The production and use of copper and copper alloys is many thousands of years old and has been based on several different production technologies over the millennia. The results suggest that copper patinas formed during different centuries exhibit variations in uniformity and corrosion protection ability. This creates micro-galvanic effects resulting both in a profound influence on the homogeneity and morphology of historic copper patinas and in a significantly increased ratio of the thicknesses of the brochantite and cuprite layers. The larger inclusions are electrochemically nobler than the surrounding copper matrix. The extent of patina fragmentation seems to depend on the size of the inclusions, rather than on their number and elemental composition. All historic patinas exhibit quite fragmentized bilayer structures, with a thin inner layer of cuprite (Cu 2O) and a thicker outer one consisting mainly of brochantite (Cu 4SO 4(OH) 6). The most common element in the inclusions is O, followed by Pb, Sb and As. The largest inclusions have a size of up to 40 μm, with most inclusions in the size ranging between 2 and 10 μm. All copper substrates contain inclusions of varying size, number and composition, reflecting different copper ores and production methods. The materials were taken from copper roofs installed in different middle and northern European environments from the 16th to the 19th century. The morphology and elemental composition of cross sections of eight historic copper materials have been explored.
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