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Metal–Crucible Interactions
Published in Nagaiyar Krishnamurthy, Metal–Crucible Interactions, 2023
The crucible has an interesting function in the ancient process known as cupellation. Native silver exists but is not commonly seen. It is usually found in nature combined with other metals, e.g. in the lead minerals galena (lead sulphide) or cerussite (lead carbonate). Silver is produced primarily by smelting and then cupellation of argentiferous lead ores. Smelting yields silver and lead combined. Lead melts at 327°C, lead oxide at 888°C and silver at 960°C. To separate the silver, the alloy is melted in an oxidizing environment at 960°C to 1000°C. The lead oxidizes to lead monoxide, known as litharge. The liquid lead oxide is removed or absorbed by capillary action into the hearth linings. The base of the hearth was made in the form of a saucepan and covered with an inert and porous material rich in calcium or magnesium, such as shells, lime or bone ash (Bayley and Eckstein 2006). A calcareous lining is essential because lead reacts with silica (clay) to form lead silicate. Lead silicate is viscous and impedes the absorption of litharge. Lead does not react with the calcareous materials. It is captured by the materials purely by the physical phenomena of absorption. Some of the litharge may evaporate, but the rest is absorbed by the porous earth lining to form ‘litharge cakes'. The litharge could be reduced back to lead separately.
The Old Ashmolean Museum and Oxford’s Seventeenth-Century Chymical Community: A Material Culture Approach To Laboratory Experiments
Published in Ambix, 2022
Umberto Veronesi, Marcos Martinón-Torres
The analysis of the residues adhering to the fragments confirms that chymical operations involving glass and zinc are by far the most prominent activities carried out at the officina chimica, where the Ashmolean chymists appear to be following an experimental approach with a wide array of ingredients, trying variants and testing different recipes. The crucible fragments with evidence of glass-related chymistry are a good example of these variations on a theme. Indeed, the scientific analysis of some of the glassy residues (Figure 2, top) identifies them as lead crystal, a type of glass invented in England towards the end of the seventeenth century and made with white sand (or crushed flints), litharge (lead oxide), and saltpetre (potassium nitrate).29 But while the composition of the Ashmolean glasses reflect the use of these ingredients their proportions vary between samples, as different ratios of ingredients were being mixed rather than combined in a standard fashion. Another way of experimenting with the lead crystal recipe was by colouring it blue, as one of the residues show, most likely through the addition of cobalt oxide, often referred to as zaffera.30 The amount of cobalt oxide necessary to tinge the glass would have been so little that its presence falls below the detection limits of the scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) employed here. However, other colourants would have required larger quantities and would have been detectable.
Lead contamination in Chinese surface soils: Source identification, spatial-temporal distribution and associated health risks
Published in Critical Reviews in Environmental Science and Technology, 2019
Yunhui Zhang, Deyi Hou, David O’Connor, Zhengtao Shen, Peili Shi, Yong Sik Ok, Daniel C. W. Tsang, Yang Wen, Mina Luo
Pb is a natural constituent of the Earth's crust, and may occur naturally and heterogeneously in soils by the natural weathering and erosion of crustal materials or via deposition of Pb emitted into the Earth’s atmosphere by volcanic activities, totally accounting for 80% of natural sources (Callender, 2003; Hou, O’Connor, et al., 2017). Forest fires and biogenic sources also contribute to soil Pb, accounting for 10% each. Pb from natural sources can be separated as atmospheric soil dust (allochthonous) or detritic source (autochthonous) (Bao, Shen, Wang, & Tserenpil, 2016). Naturally derived lead in soil is commonly in the form of gelena (PbS, logKsp = −27.5) and in smaller quantities in cerussite (PbCO3), anglesite (PbSO4), pyromorphite (Pb5(PO4)3Cl), crocoite (PbCrO4), litharge (PbO) and Massicot (PbO) (Ruby, Davis, & Nicholson, 1994; Mulligan, Yong, & Gibbs, 2001; Laperche, Traina, Gaddam, & Logan,1996). Pb usually coexists with copper, zinc and silver, and the metallic form of Pb in nature is rare (Cheng & Hu, 2010).
Substrates and preparation layers under the wall paintings of the St George’s Cathedral (1119 CE) at Veliki Novgorod
Published in Surface Engineering, 2023
Alessandra R. G. Giumlia-Mair, Vladimir V. Sedov, Olga Etinhof
The last red pigment in use at this time was minium (lead oxide, Pb3O4), both the natural and the artificial kind, obtained by heating lead minerals such as litharge and cerussite to ca. 425 and 430°C. However, no lead could be detected in the red layer under the intonachino. The EDS analyses on several areas of the red layer showed the typical peaks of ochre or, better, red earth, because it contains many impurities (Ca, Si, Al, Cl, K, Ti, Mg) (Figure 11). Therefore, we can safely conclude that the red pigment applied under the intonachino was red ochre, i.e. hematite (Fe2O3) or/and goethite (FeOOH), mixed with alumino-silicate as kaolinite or illite, quartz and calcium compounds.