Column: The crucible

Philip Ball gets down to earth with chemical archaeologists

As chemistry became a quantitative and systematic science in the nineteenth century, it began to cast a probing spotlight on the mixture of craft and confusion from which it had emerged. Armed with an increasing understanding of the elements and the properties of their compounds, chemists began to discern both the wisdom and the folly of their predecessors.

One such instance was the legendary medicine called Lemnian Earth, extracted from a single location on the Aegean island of Lemnos. There were countless approving references to this substance in old medical texts. On a visit to Lemnos, the Roman doctor Galen said that he took away twenty thousand ’seals’, the little tablets of hardened Lemnian Earth stamped with an authenticating imprint by a priestess. Both Galen and his near-contemporary Dioscorides recommend the medicine for curing dysentery, while Pliny says it also counters poisons and snake bites, and soothes inflammation. Sophocles has the eponymous hero of his play Philoctetes saved from snake venom by this medicine during the Trojan war.

But when Lemnian Earth was studied in the nineteenth century by Martin Klaproth and others, they found nothing but a silicate clay - harmless enough, but hardly medicinal. By 1914, the chemical historian Charles Thompson declared that its supposed virtues were mainly due to its mystical origins.

That has tended to remain the modern view - until now. In a paper inArchaeometry  , Allan Hall and Effie Photos-Jones of the University of Glasgow offer a new interpretation of Lemnian Earth, suggesting that there may have been a sound basis for its medical use. Ideally, one would analyse samples using modern chemical techniques that could detect ingredients invisible to cruder, older methods. But doing that with extant museum samples would be inconclusive, because there’s no way of knowing if they are genuine: fakes were widespread because of the medicine’s great value. 

Geological ritual 

So Hall and Photos-Jones have tried to deduce what Lemnian Earth might have contained, based on studies of the local geology in the light of the practices used to make the material. This latter point is the key. Lemnian Earth was not just a substance dug from the ground; it was prepared in a ritualistic way. It’s tempting to dismiss this as more superstition, but in fact the process might have wrought significant changes in the raw ingredient. 

Several accounts of the ritual exist. They don’t all agree, but some features are consistent. The substance was extracted only on one day in the year (St Saviour’s Day, 6 August), from pits that had previously been flooded with water from a diverted stream. There were various grades of Lemnian Earth in the silty sediment of the pit, and only the topmost layers were deemed to have medical potency. 

Lower grades were used to clean clothes, which suggests that the clay montmorillonite, often sold as fuller’s earth, was a major component. Another component may have been the fine-grained white clay kaolin.  

Mouth-wash not hogwash 

But Hall and Photos-Jones think the crucial ingredient was alum: soluble hydrated aluminium sulfate, widely used throughout history as a pharmaceutical. It is astringent with possible antibacterial properties. Alum has been advocated even in modern times as a mouth-rinse and deodorant. The researchers think that alum could have been dissolved in the local spring water and then concentrated in the pit sediment by absorption on montmorillonite. A final inert component, haematite, would explain the assertions that Lemnian Earth was reddish in colour, or, combined with kaolin, flesh-pink. 

This is consistent with the geology of the extraction region. The real test would be to prepare a material synthetically with the approximate composition estimated by Hall and Photos-Jones, and see if it is medically active. But the researchers’ main point is that chemical archaeology cannot afford to neglect apparently arcane or superstitious practices. Archaeological materials scientists, they say, must consider artefacts not as bare chemical entities but as objects created within a specific social milieu. It’s possible that ancient chemists may have had, in some sense, good reasons for doing things the way they did. 

Philip Ball is a science writer based in London, UK