The Palette/green/Made in a lab or a works

Scheele's green

The first cheap bright green, made of arsenic, and Victorian Britain put it on the walls, in the dresses, on the sweets and in the toys.

Also called copper arsenite · Schloss green

Hex: #6EA24A
RGB: 110, 162, 74
First used: 1775
From: Sweden

What it is

Copper arsenite, roughly CuHAsO₃.

How it is made

Carl Wilhelm Scheele made it in 1775 by combining sodium arsenite with copper sulfate. Cheap, simple and spectacularly bright compared with anything else available, which at that point was verdigris, malachite or a mixture.

Scheele knew it was arsenic and said so. He decided the commercial value justified it, which is a decision worth sitting with. Emerald green (Paris green, Schweinfurt green) followed in 1814, was a copper acetoarsenite, was brighter and more stable, and took over most of the market.

Scheele's green, Highly toxic arsenic-based pigment. Wikipedia's description, not ours.

The history

The nineteenth century put arsenic greens into wallpaper at enormous scale (estimates of a hundred million square metres of arsenical wallpaper in Britain) and also into dress fabric, artificial flowers, candles, children's toys, book cloth and confectionery. The Bradford humbug poisoning of 1858 killed at least twenty people through a confectioner's error involving arsenic, and while that particular case involved arsenic trioxide rather than the pigment, it is what finally moved public opinion.

The specific horror was the wallpaper. Damp rooms with arsenical paper grew moulds that metabolised the pigment into trimethylarsine, a volatile arsenic gas, and people sickened in their own bedrooms without any obvious cause. Nursery papers were among the worst affected. The mechanism was worked out in the 1890s by Bartolomeo Gosio, which is why the gas is sometimes called Gosio's gas.

Then there is Napoleon. The claim that the green wallpaper at Longwood House on St Helena poisoned him has been argued over for a century, and it is entirely plausible: arsenic has been found in his hair and the wallpaper was arsenical. It is also not proven. Arsenic was in everything at the time, and the medical treatment he received would on its own account for a great deal. An excellent story, with real evidence and no verdict.

Where it is used

Wallpaper, dress fabric, paint, paper, toys, book cloth and confectionery in the nineteenth century. Emerald green was also sold as an insecticide and a rat poison, which is a clearer statement of what it was than any of its other uses.

The industry knew. William Morris's family fortune came from an arsenic mine and Morris himself dismissed the wallpaper scare as hysteria for years, while eventually quietly moving his own firm to arsenic-free pigments. It is the sharpest available reminder that 'no evidence of harm' is very often a commercial position rather than a scientific one.

Go and look at it

Arsenical wallpaper samples
The National Archives, Kew: the Bitter Green collection; Winterthur, Delaware
Tested, catalogued and handled with precautions. You can look up whether a pattern is poisonous.
Longwood House
St Helena
Napoleon's rooms. The most famous wallpaper in toxicology, and the case is still open.

How it behaves

Made of: Copper arsenite, roughly CuHAsO₃.
Opacity: Opaque. It covers what is under it.
Lightfastness: Moderate. It will move, noticeably, within decades, faster in thin films and tints.

Hazard

Copper arsenite. Acutely poisonous. Generates volatile arsine gas in damp conditions with mould.

Blackens on contact with sulfide pigments, it cannot sit next to cadmium or vermilion.
Darkens over time on its own.
Still present in nineteenth-century wallpapers and book cloths; some libraries now handle them with gloves.

The numbers

All derived from the hex, never typed beside it

HEX: #6EA24A; What a browser and a design file want.
RGB: 110, 162, 74; The same three numbers in base ten. Light, not ink.
HSL: 95°, 37%, 46%; Hue, saturation, lightness, how a person describes a colour.
CMYK: 32, 0, 54, 36; Arithmetic only. A real separation depends on the press, the paper and a profile.
LAB: 61, -33, 40; Perceptual. L* of 61 is how light this actually looks, which HSL gets wrong.

This hex is an approximation, and a page about pigment has to say so. Scheele's green is a substance. A ground mineral scatters light from thousands of separate grains at slightly different angles, and no single sRGB value is that event. It is a flat average of a photograph of it, and the real thing is outside what a screen can emit. Use the number to specify a screen colour. Do not use it to judge the pigment.

Where it sits on the wheel

Hue 95°

Its opposite, by the diagram

#6EA24A

#7E4AA2

The arithmetic opposite, 180° round in HSL. Useful, and not the same as the opposite a painter mixing pigment would name, that wheel was built for paint.

Lighter and darker

Towards white

#6EA24A

#84B065

#9ABE80

#B7D1A5

#D4E3C9

#E9F1E4

Mixing with white does not only lighten, it dulls and cools. This is why a pale tint of a brand colour so often looks chalky, and why a designed light shade beats a generated one.

Towards black

#6EA24A

#5E8A3F

#4D7134

#375125

#213116

#11180B

Mixing with black kills the hue as it darkens. A better dark is usually the colour plus its neighbour round the wheel, which is what every painter does instead.

Can you set type on it

Handgloves

White on it
3.03:1 · Large text only

Handgloves

Black on it
6.93:1 · AA

Handgloves

It on paper
2.88:1 · Fails

Handgloves

It on ink
6.04:1 · AA

4.5:1 is the floor for body text and 3:1 for large text, by WCAG. Treat it as a minimum you may not go under rather than as a target: plenty of pairs pass at 4.6:1 and are still unpleasant to read for a page, and the checker will not tell you that.