archaeometallurgy

Image 1: The series on slag microscopy you will tell you about how to prepare, describe and interpret polished sections of slag samples. After that you to get hold of a microscope and invest time…

This is the first article of a series on slag microscopy. Excuse me, on what?

Yes you did read correctly: I said slag microscopy. –

This will be a series of articles thought as an introduction to the most noble and useful art of slag microscopy, the equipment needed to do slag microscopy and what slag microscopy is all about. Today’s topic is sample preparation! Slag microscopy is a small but fun part of one the most fascinating disciplines of archaeology: archaeometallurgy (:  and it is very useful for us archaeometallurgists, too.

Why? Because slag tells us a lot about the processes and products of which slag is a by-product. In order to be able to tell what slag tells us we need to have a look at it through the microscope. We have to prepare a polished section and will describe the microscopical appearance of the sample under the polarising reflected light microscope.

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Another superlative from in Pločnik in Serbia: This time the team of the Rise of Metallurgy project has found evidence for the earliest known tin-bronze. The recovered artefact, a thin sheet bronze fragment, is at least 6500 years old and consists of a copper-tin alloy with 11 wt% tin, and a number of minor elements . Archaeologists call copper alloys with zinc brass, all others are often labelled as bronze. In order to clarify that it is bronze in the sense of the modern definition, in archaeological texts it is often referred to  as tin-bronze. Alloys with arsenic are called in the rest of the best arsenical copper. Continue reading

Gossan is a term from mineral economics. The gossan may also be called iron cap. This is so because it denotes a concretion of iron hydroxides that has formed on top of sulphide mineral vein, where it reaches the surface. It forms during the supergene sulphide ore enrichment, when weakly acid surface water perloctaes through the mineral deposit. Many sulphide ores are oxidised in this process and brought into solution:

Schematic view of a sulphide vein. You can see the oxidation zone, consisting of the gossan, the leached zone and the oxidised zone. The reducing zone consists of the enrichment zone and the area of ​​primary mineralization. Significantly modified after Evans (1992) and Ottaway (1994).

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