At the end of the 18th century and the beginning of the 19th, there were two eminent botanical and natural illustration figures in the United Kingdom, who also shared a first and last name: both were called William Hooker .

One of them, whose middle name was Jackson , born in 1785, went on to direct the most important botanical garden of his time, the prestigious Kew Gardens . Father of the brilliant Joseph Dalton Hooker , also a botanist and director of Kew Gardens after his father. The same Joseph Dalton Hooker who, along with Thomas Henry Huxley, encouraged his friend Charles Darwin to make his theory public.

However, only six years older, there was another William Hooker —this one without a middle name—, not so relevant in the world of plant studies, but one of the greatest references in scientific illustration , and particularly, illustration botany. It is on this lesser-known William Hooker, born in 1779 and died in 1832, that today we will focus our attention.

Looking for the perfect color

Since ancient times, many artists have used green pigments for their creations. Most were obtained directly from mineral sources, such as malachite green , obtained from pulverizing the ore; the verdigrises , from copper acetates; earth green, obtained from glauconite or celadonite; or Rinmann’s green , based on cobalt and zinc oxides. Other synthetic green pigments were developed more recently. Among them, Scheele’s green , synthesized in 1775, and whose chemical composition is copper acid arsenite; or the green of Paris or emerald green, copper acetoarsenite, synthesized in 1814. The use of the latter was prohibited as a pigment due to its high toxicity, although it continued to be used as an insecticide until well into the 20th century.

But all these pigments, which were very useful for artistic pictures and paintings, could not match the tone of living plants. Botanical illustrators had to resort to a palette that did not accurately reflect the actual colors of what they were trying to illustrate. In addition, the mixture of those greens with other pigments gave very different tones than expected. So William Hooker, the official artist for the Botanical Horticultural Society , set out to find a solution to the problem.

What Hooker needed, in fact, was not a specific green for each plant. In nature there is an enormous variety of greens, the color of a laurel leaf is not the same as that of an apple tree, that of a beech, that of a lime or that of a cypress. What Hooker was looking for, in fact, was a pigment that would serve as a base , with an optimal color composition to obtain, through simple mixtures, a wide range of greens that faithfully represented the chromatic richness of nature.

Hooker’s Green

Hooker originally found his color by mixing in very precise proportions two pre-existing pigments, gutagamba (yellow) and Prussian blue . This composition was widely used by William Hooker himself, as well as many other contemporary botanical illustrators—including his namesake, the director of Kew Gardens.

It became such a versatile green that during the 19th century, especially in the mid-to-late century, Hooker’s green was used in almost all landscape paintings of the time , to color vegetation. The realist landscape painter Carlos de Haes , teacher of the Landscape Chair at the San Fernando Academy of Fine Arts in Madrid, used Hooker green in almost all his landscapes. Many of his paintings can be seen today in the Prado Museum .

However, over time a difficulty appeared caused by one of its components.

Guttagamba is a yellow pigment obtained from the resin of plants of the gutiferous family and, like most pigments of plant origin, it oxidizes and degrades over time . This drawback caused Hooker’s green-colored illustrations to lose their original color over time.

Hooker’s New Greens

For this reason, some time later, new mixtures were developed, based on the original Hooker green, but substituting gutagamba yellow for other non-perishable pigments.

Thus new ‘permanent’ Hooker greens were created. Currently, they are composed of phthalocyanine as a blue-green component and two different yellows, which give rise to two different Hooker greens. A lighter and brighter green —called Hooker green 1—, with a grassy tone, made with Winsor yellow , and a darker and deeper one — Hooker green 2—, with nickel yellow .

References:

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Palma, E. et al. 2021. Introduction bias: Imbalance in species introductions may obscure the identification of traits associated with invasiveness [Preprint]. Ecology. DOI: 10.1101/2021.03.22.436397

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