# Alum

**Alumen**

**Known today as.** Potassium aluminum sulfate.

Kind: Mineral

## What was it used for?

A styptic for bleeding and a drying wash for ulcers and the gums; above all, the mordant that fixed dyes.

## What does modern science say?

Genuinely astringent and styptic; still used in shaving blocks. Alum tightens the proteins of skin and blood, which is why the styptic pencil stops a shaving cut; it is the mordant that lets natural dyes take, the flocculant that clears drinking water, and the base of the aluminium salts in antiperspirants. English bakers whitened bread with it until the adulteration acts of the nineteenth century.

## Pharmacognosy and toxicology

- **potassium aluminium sulfate**: 

**Mechanism.** Aluminium ions cross-link proteins at the surface: astringency and the stopping of small bleeding.

**Dose.** Non-toxic in use; grams by mouth irritate.

**Standing.** In styptic pencils, antiperspirants, and water treatment.

## What lore surrounds it?

Until Giovanni da Castro found the alum of Tolfa in 1461 the whole supply came from the Turkish lands, and the Pope made the new mine a crusade: alum bought from the infidel was forbidden under pain of excommunication. In Yorkshire the alum shale was burned for a century from 1600 and the liquor set with human urine, shipped from London in barrels, and the cliffs of Ravenscar are still red with the waste.

## What did the older authorities say?

**Tolfa.** The discovery of alum near Tolfa in the 1460s gave the papacy a profitable monopoly, defended with excommunication.

**Herodotus.** Records that Amasis of Egypt sent a thousand talents of alum toward the rebuilding of the temple at Delphi, the first notice of it as a thing of value.

**Pliny.** Distinguishes many kinds of *alumen*, gives it to stop bleeding and to check the spread of ulcers, and says the dyers can do nothing without it.

## Sources

- Pliny, *Natural History* XXXV.
- Herodotus, *Histories* II.180.
- Pliny, *Natural History* XXXV.

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*Alum.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-01. The Thinking Press. https://thethinkingpress.org/materia-medica/alum

Historical description, not medical advice.