# Terra sigillata

*Lemnian earth, “sealed earth”*

**Known today as.** A clay dug on the island of Lemnos and stamped with a seal.

Kind: Mineral

## What was it used for?

The antidote clay: against poisons, bites, and the plague.

## What does modern science say?

Some clays bind toxins in the gut, which may explain part of its fame.

## Pharmacognosy and toxicology

- **kaolinite and smectite clays**: 
- **iron oxides**: 
- **alum**: in some sealed earths

**Mechanism.** A clay like Armenian bole: it adsorbs, dries, and firms the stool, and its smectite component binds some toxins and bacteria in the gut, as diosmectite does today. Analysis of surviving Lemnian earth tablets (Photos-Jones, 2008) found an ordinary illite-kaolinite clay. The seal guaranteed the source, which was the first trademark of a drug.

**Dose.** Safe; some clays carry lead and arsenic.

**Standing.** Obsolete as a brand; the clay class survives as kaolin and diosmectite.

## What lore surrounds it?

The seal was a guarantee against counterfeits, which were everywhere; in later centuries it was the Ottoman sultan’s.

## What did the older authorities say?

**Galen.** Sailed to Lemnos to see the earth dug and sealed by the priestess, and brought twenty thousand of the stamped tablets home.

## Sources

- Galen, *On the Powers of Simple Medicines* IX.
- Photos-Jones, E., and Hall, A. J. (2011). *Lemnian Earth and the Earths of the Aegean: An Archaeological Guide to Medicines, Pigments and Washing Powders*. Potingair Press.
- Dupont, C., and Vernisse, B. (2009). “Anti-diarrheal effects of diosmectite.” *Paediatric Drugs* 11.

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*Terra sigillata.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-09-25. The Thinking Press. https://thethinkingpress.org/materia-medica/terra-sigillata

Historical description, not medical advice.