Mordant dyeing: alum fixes the colour
A dyeing procedure in which a fast colour comes not from the dyestuff itself but from a third substance, the mordant, which binds fibre and dye. Pliny in the Natural History describes this as an Egyptian marvel: cloth is saturated with something that does not colour it, is dipped in a single vat and comes out many-coloured.
The mordant also governs the colour itself: madder with alum gives red, with iron violet, with chromium a brownish red, so that one and the same dyestuff yields different tones under different salts. For centuries the craft worked with solutions, precipitates and weighed proportions without any theory of them.
At the same time the dyers made lake pigments for painting out of dyestuffs and alum; it was from such a lake, short of potash, that Prussian blue later came.
Why this date
Approximate, and it is the date of the evidence, not of the invention. The axis value is the year of Pliny's Natural History (77 CE), which describes the Egyptian practice: white cloth is saturated with preparations that do not colour it but absorb colour, after which a single vat yields a many-coloured cloth. The same book says which kinds of alum are used for wool of bright and of sombre tints. The practice is certainly older: the word stypteria (alum) is already read in the Linear B tablets from Pylos, though the tablet does not say what it was used for (University of Glasgow project archive, citing Hall et al., 2003). No chemical account of how a mordant works existed before the eighteenth century.
What grew out of it
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Prussian blue: the first purely synthetic pigment
influenced · Confidence: medium
The blue came down inside the recipe for a lake pigment which, like mordant dyeing, used alum: Diesbach was precipitating a cochineal extract with alum, iron sulfate and potash, and it was the iron of that recipe which, with the spoiled potash, gave a blue precipitate instead of a red one.
Dispute: The whole account of the circumstances goes back to Stahl's book of 1731, that is, it was written down a quarter of a century after the event and not by a participant. Kraft, while giving it as the most probable version, says in the same breath that the discovery is still enigmatic and has not been well researched, and that Stahl gives no date. The link is therefore exactly as firm as Stahl is.
Link sources
- Kraft A. «On the Discovery and History of Prussian Blue», Bulletin for the History of Chemistry 33 (2), 61-67 (2008), 61-62 Verified 25 Sep 2026
Diesbach was attempting to produce Florentine lake, a red pigment based on cochineal red. Usually he did this by precipitation of an extract of chochineal (produced by boiling dried cochineal insects with water to extract the carminic acid) with alum (KAl(SO4)2.12H2O), iron sulfate ("Vitrioli Martialis"), and potash ("Sale alcalico Tartari").
- Kraft A. «On the Discovery and History of Prussian Blue», Bulletin for the History of Chemistry 33 (2), 61-67 (2008), 61-62 Verified 25 Sep 2026
However, having no more potash, he borrowed some from Dippel that had been used in his animal oil production. This potash was contaminated with hexacyanoferrate; and therefore the addition of contaminated potash to the solution, which already contained iron sulfate, resulted in a blue precipitate
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Kraft A. «On the Discovery and History of Prussian Blue», Bulletin for the History of Chemistry 33 (2), 61-67 (2008), 61-62 Verified 25 Sep 2026
Node sources
- «Естественная история», XXXV, 42, Bostock and Riley Perseus (77) Verified 20 Sep 2026
After pressing the material, which is white at first, they saturate it, not with colours, but with mordents that are calculated to absorb colour.
- «Естественная история», XXXV, 52, Bostock and Riley Perseus (77) Verified 20 Sep 2026
the white liquid alumen being employed for dyeing wool of bright colours, and the black, on the other hand, for giving wool a tawny or a sombre tint.
- University of Glasgow, «Earths of the Aegean: Melos, Melian alum» (2003) Verified 20 Sep 2026
as well as being used as a mordant for fixing dyes, it is astringent and has anti-bacterial properties
- University of Glasgow, «Earths of the Aegean: Melos, Melian alum» (2003) Verified 20 Sep 2026
Pliny in the 1st century AD gives a detailed account of the many 'genera' and 'species' of alumen and its many applications.
- Encyclopaedia Britannica, «alizarin» (2024) Verified 24 Sep 2026
requires prior impregnation of the fibre with a metal oxide, or mordant
- Encyclopaedia Britannica, «alizarin» (2024) Verified 24 Sep 2026
aluminum yields a red; iron, a violet; and chromium, a brownish red
- Kraft A. «On the Discovery and History of Prussian Blue», Bulletin for the History of Chemistry 33 (2), 61-67 (2008), 61-62
Usually he did this by precipitation of an extract of chochineal (produced by boiling dried cochineal insects with water to extract the carminic acid) with alum (KAl(SO4)2.12H2O), iron sulfate ("Vitrioli Martialis"), and potash ("Sale alcalico Tartari").
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.