Mind your own beeswax – Insights into the composition of the Nimrud writing tablets – The Past

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In ‘Science Notes’, we often talk about how new technologies are revolutionising our approach to archaeology. And while this is most certainly still the case, the reliability of previous methods can sometimes be taken for granted. This month we are considering research recently conducted at the British Museum on the famous Nimrud Tablets, which proves just how accurate research done almost 70 years ago can be, while also showcasing how the latest technologies are continuing to provide significant insights that enhance our overall understanding of the past.

The Nimrud Tablets were discovered at the bottom of a well during excavations at the site in present-day Iraq during the 1950s. They are thought to have been thrown there during the sacking of the Assyrian city in 612 BC. Although they have been in the British Museum’s collections ever since, a few years ago they were scheduled to be moved, and curators wanted to know how safe it was to handle them, as some of the 1950s reports had stated that they contained arsenic in the form of orpiment – a yellow pigment made from arsenic sulfide.

The reports mentioned that the tablets had been analysed by Dr H J Plenderleith shortly after they were first acquired by the museum and that he found that the writing surface of the tablets was made from beeswax mixed with orpiment. The specific methodology that led him to this conclusion, however, is unknown, the records having since been lost. The wood backing of some of the tablets was also analysed by D Evans from the Forest Products Research Laboratory at Princes Risborough in 1953, who identified it as walnut. As with the writing surface, the methods used are unknown.

To confirm whether these 70-year-old identifications were correct and whether modern techniques can reveal more information about the tablets, scientists from the Department of Scientific Research at the British Museum, led by Dr Diego Tamburini, took three new microsamples from writing materials either on or associated with the tablets: one sample came from yellow writing paste detached from the surface of the boards (sample Y), another was taken from an area of one of the boards characterised by a whitish residue (sample W), while the last was taken from a black residue also present on the writing surface of one of the boards (sample B). Additionally, four samples of wood were taken.

The team then analysed the writing surface samples, first using FTIR (Fourier-transform infrared spectroscopy) to obtain a general identification of the classes of materials present, and then subsequently using more targeted techniques to determine the specific composition of each sample. The FTIR analysis revealed that, apart from burial environment contamination, all three samples were probably composed of beeswax, and sample B had a profile also consistent with the addition of carbon black from charred plant matter. This was an intriguing discovery, as the addition of carbon to wax writing tablets is currently unknown from before the Greek and Roman civilisations. If this was indeed added as a form of pigment, it would mean this technique was being used much earlier than originally thought. More research would need to be done to confirm this, though, as it was only found in one sample.

Gas chromatography-mass spectrometry, meanwhile, confirmed that the beeswax was probably pure, without any oil or other additive present. Raman spectroscopy was able to confirm the 1950s finding of the use of orpiment, too. Finally, the wood from the tablets was analysed using scanning electron microscopy (SEM), comparing the Nimrud samples with a database. This confirmed that the wood used was definitively walnut, in line with its 1950s identification. As this tree grows throughout south-west Asia, it is probable that the wood was sourced locally.

Unlike the 1950s results, however, the modern analysis was able to go further than just the identification of material. The gas chromatography results showed that the beeswax had little degradation, suggesting that for its age it had outstanding preservation. There were only small signs of hydrolysis of the wax, much less than was found in the Bloomberg wax writing boards from Roman London for example (see CA 317), which were found in a completely water-logged burial environment. The team suggest that this excellent preservation may be due to the complex conditions the Nimrud tablets were buried it, which would have originally been waterlogged but then dried in low oxygen conditions over 2,500 years. The team also hypothesise that the presence of orpiment could have further aided their preservation. Arsenic is known for its anti-microbial activity and could have prevented the spread of bacteria. Indeed, preliminary evidence from other contexts suggests that artefacts containing orpiment or other arsenic-containing pigments may be unusually well- preserved. Further research would need to be done to confirm this hypothesis, however.

Ultimately, this research demonstrates that, whatever methods were used in the 1950s, they were incredibly accurate, but that more modern techniques are even more insightful, particularly in helping with the conservation of the objects, establishing how better to preserve, conserve, and display them.

Text: Rebecca Preedy / Image: The Trustees of the British Museum



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