Slag analysis in archaeology draws almost exclusively from Earth science methods, primarily geochemistry, ore petrology, and igneous petrology. Ideally, this involves a multielement fully quantitative chemical method such as X-ray fluorescence (XRF) or inductively coupled plasma (ICP) spectrometry in combination with optical and electron microscopy for a qualitative or semi-quantitative assessment of miner-alogical parameters. In reality, costs of analysis and ease of access to, or availability of, instruments and expertise often play a decisive role in selecting methods of analysis. For all quantitative methods it is imperative to monitor and report data quality (accuracy and precision) through publishing results for analysis of certified reference materials along with the unknown samples, in order to be able to compare data from different laboratories.
Smelting slag often occurs in huge quantities, measuring in tons or even thousands of tons; the main practical considerations here are sample size and rep-resentativity. Sampling methods developed for Earth sciences are often appropriate, including sampling of stratified profiles and reducing large sample volumes through homogenization and quartering into aliquots suitable for the chosen instrument. Curatorial constraints are often more important in the analysis of other waste materials, such as crucible fragments, which have a stronger developed object character and do not occur in such large quantities. Here, crosssections prepared for reflected light microscopy (RLM) and scanning electron microscopy (SEM) with attached energy dispersive spectrometry (EDS) are more suitable than bulk chemical analysis. SEM-EDS has relatively high detection limits in the order of 0.1wt.% for most elements, and therefore provides only limited chemical information; however, it offers a high spatial resolution of what is analyzed, ideal for complex and multiphase materials such as crucibles with internal slag and external vitrification. A balance between the curatorial desire to minimize the sampling impact and the analytical need for a representative sample is sometimes difficult to achieve, and may require the use of noninvasive and nondestructive methods such as surface-XRF or micro-XRF.
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