Experimental Archaeometallurgy

Presentamos en este trabajo un balance de los experimentos sobre funcionalidad de los instrumentos metálicos, desarrollados a lo largo de los últimos años en la Universidad Autónoma de Madrid. En él insistimos en la necesidad de precisar el protocolo experimental así como evaluar las aportaciones reales que este tipo de procedimientos proporciona a la comprensión del pasado.

This paper relates to a study of experimental archaeology, executed by Ruben Cataldo, about the forging methods used to produce some replicas of two metal points found during the archaeological excavations carried out between 1992 and 1996 by the University of Salento in the medieval village Quattro Macine (translated Four Millstones), located in the municipality of Giuggianello, a small town in Southern Apulia (South-East Italy). This study has been made by forging several replicas of these two particular finds, describing the step by step forging process of both artefacts. The study also focused on the interpretation problem between arrowheads and crossbow bolt heads, reflecting on the differences between the two types of weapons, and trying to formulate an idea of how to properly interpret the artefacts, to guarantee a certainty on this kind of analysis. The interesting thing about these two points is that not many similar finds have been discovered in the whole area, and none have been found in rural settings like Quattro Macine. For this reason, this study has been made with the aim of trying to understand whether these heads were forged in situ or if they were imported products, and moreover to understand why the village's inhabitants needed them (Cataldo, 2017).

Presented at European Textile Forum 2018, Mayen.
A brief introduction to experimental work undertaken at the conference.

Previously this study has demonstrated the importance of metal choice for construction of a dyeing apparatus - it was found that even materials that had been mordanted and dyed were heavily influenced by the kettle material. This complete re-run of the dyeing experiment confirmed the original visual findings, while also giving samples of mordants, dyes, fabrics and yarns that can now receive chemical analysis to see the absorption of each type of metal (lead, lead oxide, iron, copper) at each stage of the dyeing process. Material samples are to be buried to allow later analysis of the impact of burial in archaeological textiles. Additionally, this experiment highlighted the need for repetition - using natural dye stuffs results in subtle variations during identical processes, which would remain undetected without repetition.

Today the advanced development of tools and methods in archaeometallurgy enables a more accurate reconstruction and understanding of ancient smelting techniques. Especially pyrometallurgical experiments allow the establishment of secure links between ores and their respective smelting products. As copper was the first metal to be smelted from ore, interest in copper metallurgy has dominated the field of archaeometallurgy from its beginning.
The aim of this contribution is to fuel the research on copper isotope fractionation during the smelting process. To analyse the fractionation behaviour seven smelting experiments with malachite were carried out in a small induction furnace and different portions of the melt were extracted from the crucible during the process.
Our results show a significant fractionation of copper isotopes during the smelting process. As predicted by the stable isotope fractionation theory, the lighter isotope is enriched in the metallic melt. Although no significant differences between ore and metal were measured, the sole appearance of fractionation questions the direct link between both. Therefore existing applications of copper isotopes in archaeometallurgy must be re-evaluated for their suitability.

It is accepted knowledge that when re-melting alloys, some of the metal with a lower melting temperature is lost through oxidation, and more metal must be added in order to maintain the desired alloy proportions. In order to understand the changes in alloy content when recycling using Bronze Age technology, experiments were undertaken by the author and others, using a charcoal furnace. These experiments included recycling bronze to quantify loss of tin, and experimentation in co-melting metals. The results were then compared to modern metallurgical practices using electric and gas furnaces. The initial results were presented at the Historical Metallurgy Society’s Research in Progress Conference in November of 2009. However, this paper includes further experiments that build on that work. The conclusions indicate that knowledge of earlier practices was lost with the advance of technology, and that broad assumptions cannot be made about earlier technological practice based on work done with modern equipment.

A peculiarity of Pyrgos’ metallurgical context is the proximity of the furnaces to the Olive Press Room and to several huge pithoi for the storage of olive oil.
This fact, added to a very unusual shape of two furnaces and to the scarcity of charcoal recovered in the combustion chambers of furnaces, produced some considerations about the nature of the fuel employed in the metallurgical process. The hypothesis of an eventual use of the olive oil (and its processing residue) has been tested by preliminary experimental trials which created a solid base to design a more accurate and scientific research protocol for the future investigation of Pyrgos-Mavroraki by Experimental Archaeometallurgy.

The work is devoted to the history of metallurgical production in Northern Eurasia during the Bronze Age, based on experiments carried out by the author and analyses of ancient slag, ore and metal. It should be noted that archaeometallurgical studies include a huge range of works reflecting different fields of activity of ancient metallurgists. Often, all that unites these is the term ‘metallurgy’. This work considers the problems of proper metallurgy, i.e. extracting metal from ore.
http://archaeopress.com/ArchaeopressShop/Public/displayProductDetail.asp?id=%7b0AD8DBA6-A46D-430A-81F2-5AB569FA5BD4%7d

In their attempts to understand the unwritten past of human technology and progression, archaeologists have borrowed aspects of the natural sciences to answer big questions. In one such pursuit, fundamental aspects of the sciences have been employed towards the chemical compositional analysis of copper-based artifacts, often to simply classify which is bronze, brass, or pure copper, and to explain why they are significant in limited space and time. This thesis takes the variety of identified metal types and compositions from these analyses and builds the beginnings of an ambitious thermodynamic model based on the accepted premise of consistent and widespread recycling of ancient metals over time. Following the laws of thermodynamics, in systems at equilibrium, the model predicts the outcome of metal losses over the course of ancient pyrometallurgical processes from molten systems through both volatilization and oxidation using rigorous and established mathematics and theory. Elemental loss likelihoods are modeled for all binary copper-based metals, using activity coefficients, and ternary copper and zinc-based systems, with the excess Gibbs free energy, respectively. The calculations are performed using custom-written software designed to account for hundreds of thousands of compositional permutations after the method described by Redlich and Kister (1948). The results of these calculations are given as activity (binary) and isoactivity (ternary) contour lines. Quantified tables for the oxidation and volatilization of elements from a copper melt at 1200 ºC and 1 atm are also given as rough indicators of element loss in ancient pyrometallurgical systems. A proof of concept of the models viability is also provided for binary Cu-M and ternary Cu-M-Zn (M = Ag, As, Au, Bi, Co, Fe, Ni, Pb, Sb, Sn, Zn), Cu-Sn-Pb, and Cu-Sb-As systems from the Late Bronze Age to post-medieval periods in Britain, which is based on several substantial artifact chemical datasets. For each ternary system, the interaction parameters used for higher-order calculations from the fitted behavior of each contributing binary systems are provided.
Comparison of the calculated models to available experimental system assessments, and to published archaeological chemical datasets, show that in both respects the proposed modeling of ancient copper-based metal losses works. And given the near ubiquity of ancient metal use around the world, the consistency in metal production and recycling technology, and the chemical analyses available, this preliminary model can be applied virtually anywhere the technology for smelting and recycling existed. In addition to loss modeling, this thesis has the additional offshoots of predicting ancient furnace conditions based on the calculated behavior of interacting metals, and of the controlling thermodynamic factors in the ancient calamine process.