Some problems and potentials of the study of cupellation remains: the case of post-medieval Montbéliard, France

Abstract

Bone-ash cupels are increasingly identifi ed in medieval and later archaeological contexts related to the refi ning of noble metals in alchemy, assaying, jewellery or coin minting. Th ese small fi nds may provide information on metal refi ning activities, the technical knowledge of diff erent craftspeople, and the versatility of laboratory practices, which often diff ered from the standard protocols recorded in metallurgical treatises. Th is paper is centred around a late 16 th -early 17 th century cupel excavated in Montbéliard, France. Th e analytical study by optical microscopy, ED-XRF and SEM-EDS allows the cupel to be ascribed to the assaying of the silver content of an ore sample, which is supported by local historical and geological information. Th e manufacture of the cupel, made of a mixture of wood ash and bone ash, is also addressed, as well as the limited technical effi ciency of the operation. Th is leads to a wider discussion of diff erent recipes for the manufacture of cupels, documented historically and archaeologically, and involving the combination of various raw materials such as bone, wood ashes and clay. Th is variability raises interesting questions about the existence of diverse technical traditions, and the material properties and performance of diff erent cupels in their specifi c contexts. In order to facilitate comparisons, we propose that the study of cupellation remains is most informative when it combines microscopy and microanalysis. Th e role of experimental approaches to these questions is also discussed. Résumé : Les coupelles en cendres d'os sont de plus en plus nombreuses à être reconnues dans des fouilles médiévales ou modernes. Elles sont utilisées pour l'affi nage de métal précieux par les alchimistes, les essayeurs, les orfèvres ou encore les monnayeurs. Ces artefacts peuvent fournir des informations sur les techniques d'affi nage, les savoir-faire et les pratiques de l'atelier qui souvent sont diff érentes des recettes et procédés décrits dans les textes métallurgiques. Cette étude concerne une coupelle de la fi n du XVI e siècle ou du début du XVII e siècles découverte en fouille à Montbéliard (France). Les analyses, par microscopie optique, MEB-EDS, et ED-XRF permettent d'associer la coupelle à l'essai d'un échantillon

Bismuth behaviour during ancient processes of silver–lead production

“…In ancient times, however, textbooks as well as archaeological remains testify that, if the usual preference was indeed for bone ash, many other recipes were used depending on metallurgical traditions or more simply due to the availability of materials: wood ash, bone ash, a mixture of the two or even clay hearths topped with a non-siliceous lining (Agricola, 1556;Bayley and Eckstein, 2006;Biringuccio, 1540;Ercker, 1580;Hawthorne and Smith, 1979;Martin on-Torres et al, 2008). All these materials may behave slightly differently during cupellation, and the formation of lead silicates or calciumesilicaephosphates is likely to diminish their capacity to absorb metallic oxides (Bayley and Eckstein, 2006;Rehren, 1998).…”

Capitalist miners in feudal Europe: A commentary on Marxist agrarian history

“…A second smelting took place in a slag‐hearth, producing “a reducing atmosphere” needed for smelting the grey slag. This was a “high‐temperature metallurgical operation aimed at refining the noble metals” (Martiñón‐Torres, Thomas, Rehren, & Mongiatti, : 60). It required melting the metal under oxidizing conditions for creating oxidized lead or litharge, in a process that worked in two ways: “it oxidized other base metals present, and reacted with metal oxides to form fusible compounds.” “As a result, the noble metals, which do not react with oxygen or lead oxide, separate from the melt as a discrete button.” A cupel or small thick vessel made of ashes from calcined bone was used for this operation.…”

Testing the New World: early modern chemistry and mineral prospection at colonial Jamestown, 1607–1610

“…Cupels were a type of specialised laboratory tool, used in postmedieval times to separate precious metals from the lead bullion into which they had been concentrated during fire assay. Upon heating, the very porous matrix of cupels, usually made with bone ash, absorbed the lead oxide and droplets of gold or silver were left behind (Martinón-Torres et al 2008a). The bulk composition shows phosphate and lime adding to 34.4 of the total wt%, with the balance being almost entirely the absorbed lead oxide (61.4 wt% PbO).…”

“…In particular, the archaeometric analysis of reaction vessels and the residues within them has proved to be a very powerful tool with regard to the reconstruction of chemical processes, the degree of technical knowledge and understanding of the practitioners and the motivations behind their activities. Pioneering research has been conducted in the field of the archaeology of early modern alchemy and chemistry especially focusing on assemblages of laboratory remains linked to metallurgical operations (Rehren 1996;Martinón-Torres andRehren 2005b, 2007;Martinón-Torres et al 2008a;Mongiatti et al 2009a, b;Martinón-Torres 2012). Relatively little work, however, has used archaeology to address developments in early modern experimental chemistry in colonial environments.…”