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Once referred to as “one of the greatest pomological artists of all time” William Hooker (1779–1832) worked as the official botanical illustrator for UK’s leading gardening charity, the Royal Horticultural Society. In need of a green that would work for depicting plants, Hooker combined Prussian blue with gamboge, and the resulting hue has since been called Hooker’s green.

But then, what is Prussian blue? And what is gamboge?

Prussian blue is the first modern synthetic pigment. It was discovered by accident in the very early 1700’s, when paintmaker Johann Jacob Diesbach (1670 – 1748) was going to make a batch of carmine lake, which normally called for powdered cochineal, alum, ferrous sulphate, and some alkali. Diesbach had run out of alkali and borrowed some that unbeknownst to him had been distilled with animal oil, and the result was that instead of the red he was trying to create he got a bright blue. Prussian blue has later been the basis of photocopying technology and has been used to create cyanotypes, an early method for photographic printing. (Prussian blue also has medicinal uses, so much so that it is on the World Health Organization’s Model List of Essential Medicines.)

Gamboge is a yellow pigment which comes from the latex of a tree that is found in Cambodia. The tree, and gamboge, can be found in other Southeast Asian countries as well, but if you say Cambodia out loud, especially if you pronounce it in French — Cambodge — and then you say gamboge, you’ll get a good understanding of how the pigment got its name.

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My sample sheet with Hooker’s Green from Winsor & Newton. And, at the bottom, a sample of Antwerp Blue and Indian Yellow (both also from Winsor & Newton) mixed together. Photo and coloring: Martin Høyem

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