Alchemical Substances
Terra Sigillata
Earth
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Terra Sigillata ("sealed earth") is a medicinal clay long classified among the "earths" of pre-modern chemistry and alchemy, historically mined at particular sites, most famously on the Greek island of Lemnos, and pressed into small tablets stamped with an official seal certifying authenticity before sale. Physicians and apothecaries from antiquity through the early modern period prescribed it as a broad remedy against poison and disease, and its status as a genuine, distinctly sourced and officially sealed mineral earth made it a standard reference substance in alchemical and pharmaceutical writing on the earths.
Facts
Physical Description
Chemical FormulaNo single fixed formula; a natural clay (aluminosilicate) earth, typically iron-rich, its exact composition varying by mining site, such as the reddish bole clay historically mined on Lemnos. 1 ToxicityLow toxicity as a clay mineral; its historical reputation rested on a supposed power to counteract poison rather than on any danger of its own, a claim modern toxicology does not support. 1 Method
Preparation MethodMined at particular sites, most famously the Greek island of Lemnos, and pressed into small tablets stamped with an official seal certifying authenticity before sale. 1 Attestation
Earliest AttestationGalen describes traveling to the island of Lemnos in the second century CE to witness the digging and official sealing of the most celebrated variety, the Lemnian earth. 1 Cross-Tradition Connections
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