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

Verdigris

Copper corroded with vinegar. The brightest green available for fifteen hundred years, and it eats the paper it is painted on.

Also called copper acetate · vert-de-Grèce · Spanish green · aerugo

Hex: #43B3AE
RGB: 67, 179, 174
First used: Antiquity; described by Pliny and Vitruvius
From: Montpellier, France, was the centre of the trade for centuries

What it is

Copper acetates, in several forms. The blue-green and green varieties are chemically different and behave differently.

How it is made

Sheets or scraps of copper are stacked in a sealed pot with vinegar (or with grape pomace, which is what Montpellier used, being surrounded by vineyards) and left for weeks. The acetic acid corrodes the metal and a blue-green crust forms on the copper, which is scraped off, dried and ground.

The Montpellier industry was a domestic one run largely by women, working the pots in cellars, and it ran for centuries on the waste of the wine trade. It is a good example of a pre-industrial chemical industry that nobody would call one.

The colour of the product depends heavily on the details, and old sources give dozens of variant recipes: with honey, with salt, with urine, with different acids. Because the product is a mixture rather than a single compound, no two batches were quite the same.

Verdigris, Green copper-based pigment. Wikipedia's description, not ours.

The history

For most of European history this was the only strong bright green. Everything else was either a dull earth, a weak mineral, or a mixture of blue and yellow, and mixtures were less brilliant. So verdigris went into manuscripts, panel paintings, glazes over gold, textiles and maps, despite everybody knowing it was trouble.

The trouble is that copper acetate is corrosive. On parchment and paper it attacks the substrate directly. There are medieval manuscripts where every green letter has eaten a hole clean through the page, so the leaf is a stencil of its own decoration. It also blackens or browns in oil over time, and it reacts with orpiment and with sulfur-containing pigments.

Painters developed a workaround: copper resinate, verdigris cooked into a resin, which is more stable and gives a deep transparent green glaze. It still browns, and a considerable number of old-master landscapes that look brown were green. The autumnal Old Master palette is partly a chemical accident that art history then mistook for taste.

Where it is used

Manuscripts, panel painting, glazes, map colouring and textiles. Also medicine and, less happily, as a pigment in food colouring and cosmetics in periods with no regulation.

It has a second life as a look rather than a pigment: the green of weathered copper (the Statue of Liberty, a church roof, a bronze) is the same family of copper corrosion products happening slowly in the open. Specifying a 'verdigris' finish today means designing for a material to change, which is a much more interesting brief than choosing a colour and is why patinated copper keeps coming back in architecture.

Go and look at it

Manuscripts with holes where the green was
Any large manuscript collection
The decoration has eaten the page. The most direct demonstration that a pigment is a chemical.
The Statue of Liberty
New York Harbour
Copper corrosion products, formed over about thirty years. The same chemistry, done by weather.

How it behaves

Made of: Copper acetates, in several forms. The blue-green and green varieties are chemically different and behave differently.
Opacity: Semi-opaque. It covers, but something of the layer beneath still comes through.
Lightfastness: Moderate. It will move, noticeably, within decades, faster in thin films and tints.

Hazard

Copper acetate is toxic if ingested and was historically a real cause of poisoning.

Corrodes paper and parchment, it eats through pages.
Browns and blackens in oil over time. Many brown Old Master trees were green.
Reacts with orpiment and sulfide pigments, blackening both.

The numbers

All derived from the hex, never typed beside it

HEX: #43B3AE; What a browser and a design file want.
RGB: 67, 179, 174; The same three numbers in base ten. Light, not ink.
HSL: 177°, 46%, 48%; Hue, saturation, lightness, how a person describes a colour.
CMYK: 63, 0, 3, 30; Arithmetic only. A real separation depends on the press, the paper and a profile.
LAB: 67, -32, -7; Perceptual. L* of 67 is how light this actually looks, which HSL gets wrong.

This hex is an approximation, and a page about pigment has to say so. Verdigris 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 177°

Its opposite, by the diagram

#43B3AE

#B34348

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

#43B3AE

#5FBEBA

#7BCAC6

#A1D9D7

#C7E8E7

#E3F4F3

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

#43B3AE

#399894

#2F7D7A

#225A57

#143634

#0A1B1A

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
2.53:1 · Fails

Handgloves

Black on it
8.30:1 · AAA

Handgloves

It on paper
2.40:1 · Fails

Handgloves

It on ink
7.23:1 · AAA

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.