An experimental approach for smelting tin ores from Northwestern Iberia

Abstract

In the present work microstructural and chemical analysis of tin and slag that resulted from three smelting experiments reconstructing prehistoric conditions are presented. Cassiterite ores were collected from northwestern (NW) Iberian deposits and were smelted in a small open pit. Results show that the loss in tin can be very high, up to 80%, mainly as a result of volatilization of Sn species. The experiments show that using handmade leather bag bellows and clay tuyeres, temperatures can easily reach >1200°C. The tin produced was a very pure (Sn) solid solution, with the presence of dispersed inclusions or phases of various composition. These included FeSn and FeSn 2 intermetallics and small metallic W inclusions. Slags could be grouped into three types based on their physical characteristics, and bulk chemical analysis could relate each type as being a product from the reaction of ore material or a product from the reaction with the crucible material. Generally, it was found that in spite of very low recovery rates, the tin produced by this simple technique would have been adequate for a domestic small-scale production. ARTICLE HISTORY

Ancient tin production: Slags from the Iron Age Carvalhelhos hillfort (NW Iberian Peninsula)

“…Recent smelting experiments made by some of the authors (Figueiredo et al, 2017) to produce tin using two sources of NW Iberia cassiterite (one of the sources was C5, Gondiães, 13 km SW of Carvalhelhos) by open and small size fire structures resulted in a very high Sn loss due to volatilisation (up to 80%). And despite the use of cassiterite ores with Ta and Nb the composition and microstructure of the resulting slags were rather different from the Carvalhelhos slags.…”

On smelting cassiterite in geological and archaeological samples: preparation and implications for provenance studies on metal artefacts with tin isotopes

“…This loss is similar to that reported by Smith (1996) for modern tin extraction and to results of the study of Zhang et al (2015) when reducing synthetic SnO 2 at 1100 °C in atmospheres containing 50-70 vol.% CO. However, the observed loss is far less than that observed in field experiments (up to 70%) with cassiterite simulating primitive prehistoric smelting operations (Earl 1986(Earl , 1994Timberlake 1994;Figueiredo et al 2017). Since our laboratory experiments used synthetic SnO 2 having no typical tramp elements of cassiterite such as iron, aluminium, silicon, niobium, tantalum etc., the preconditions are hardly comparable.…”

“…Besides the characterisation of tin ores for provenance studies, the next step in our research would thus be designed like D. Bourgarit's and N. Thomas' study 'From laboratory to field experiments' (Bourgarit and Thomas 2011). For this purpose, products from cassiterite smelting obtained in field experiments by Figueiredo et al (2017) and bronzes from melting and casting experiments are currently being evaluated (Berger et al unpublished data).…”

Al Calor Del Fuego: La Didáctica Mediante La Arqueometalurgia Experimental Y Experiencial

“…La segunda conocida como cementación consiste en la obtención de la aleación mediante la reducción de minerales de estaño sobre cobre metálico. La última de las fórmulas posibles de obtención de bronce es la reducción por separado de minerales de cobre y estaño, para su posterior aleación Las actividades que hemos desarrollado han explorado de forma experimental estas tres posibilidades de forma positiva, permitiéndonos profundizar en la metalurgia extractiva desde una perspectiva empírica Figueiredo et al, 2017).…”

“…También han sido realizados análisis isotópicos de estaño en el ámbito de una colaboración internacional con el proyecto proyecto Bronze Age tin -Tin isotopes and the sources of Bronze Age tin in the old World (ERC project). Los resultados de estas investigaciones están siendo presentados en diversos foros nacionales e internacionales (Berger et al, 2018;Figueiredo et al, 2017).…”