Quantitative chemical analysis of archaeological slag material using handheld X-ray fluorescence spectrometry

Handheld X-ray fluorescence spectrometry (XRF) has seen a dramatic increase in use for archaeological projects. The attraction of the technique is its portable and nondestructive nature. In many cases, the archaeological artefacts in question cannot be destructively sampled, or the piece itself cannot be sent to an analytical laboratory. One of the current research interests associated with the Sagalassos project is the study of the Roman iron industry. Previously exported iron slag and ore from the site and the surrounding area was subjected to laboratory chemical analyses. These indicated that different ores were being utilized in the production of iron in different periods. In order to further the project the slag material still in the site depot needed to be analyzed. However, recent legislative changes mean that materials can only be analyzed on-site. Since samples could not be taken and destructive chemical analysis was no longer feasible, a portable, nondestructive technique was required. Handheld XRF can easily provide qualitative data, but these data are only comparable to other handheld XRF qualitative data, from the same device. Quantitative data gathering is possible, but can be more problematic, particularly when the material in question is heterogeneous in nature. A calibration file was created using the manufacturer’s software and “in-house” standards made from the pre-quantified samples of iron slag available in the laboratory. In order to make the calibration as robust as possible, the composition of the standards was analyzed statistically to determine which of these created bias and leverage for specific elements. These standards were then omitted from the calibration for that element. The calibration was tested in the laboratory using samples of iron slag previously analyzed with wet chemistry, and the results indicated that most sample analyses showed &lt;30% error. Results with a &gt;30% error were found in samples which contained very low or very high quantities of the analyzed element, i.e., outside the limits of the calibration. The handheld XRF and the associated calibration file were then used to provide a semi-quantified chemical characterization of the samples in the field depot. </jats:p

Experimental mixing of natron and plant ash style glass: implications for ancient glass recycling

The practice of re-melting glass was well known, certainly from the Roman period onwards. This can be seen not only in ancient literary evidence but also in the archaeological evidence, collections of broken glass have been found in, for example, Pompeii (79 AD) and the Iulia Felix shipwreck (Third century AD). Elevated levels of certain transition metals in archaeological glasses are interpreted as indications of the mixing and/or recycling of different glasses. Assumptions have been made that all glasses could be recycled, but to what extent are these valid? Why does the evidence for the recycling of glass only occur from the Roman period onwards? From the middle of the First millennium BC to the Ninth century AD, natron glass was the predominant glass type in the Mediterranean and Europe, however, plant ash glass was still in use in some areas. To test the effects on the final product of mixing different composition glass types, experimental glasses were made by mixing varying quantities of replica plant ash glass, replica natron glass, and a modern glass. At low temperatures crystalline material formed in the products containing replica plant ash glass. As the plant ash glass content increased, so too did the amount of crystalline material produced. This is due to a combination of the glass compositions and the firing temperature. It appears that natron type glass can be more easily recycled at lower temperatures, although, if a high enough temperature is used then most glass types can be recycled. Early furnace technology, i.e. the vertical heating chamber furnace, may not have been able to achieve these high temperatures, hence the widespread practice of recycling did not begin until after the invention of glassblowing which required a change in the furnace technology to the use of a horizontal heating chamber furnace