The Palette/green/Made in a lab or a works
Viridian
The first bright green that will not poison anybody: cool, transparent, permanent, and it ended the arsenic era in a single generation.
Also called Guignet's green · hydrated chromium oxide
- Hex
- #40826D
- RGB
- 64, 130, 109
- Pigment index
- PG18
- First used
- 1838, patented 1859
- From
- Paris
What it is
Hydrated chromium(III) oxide, Cr₂O₃·2H₂O.
How it is made
Chromium compounds are calcined with boric acid and the product is washed. Pannetier made it in 1838 and kept the method secret; Guignet patented a practical process in 1859, which is why the French name for it is vert Guignet.
The related opaque version, chromium oxide green (PG17), is made by firing without the water and is a much duller, denser, army-green. The two are chemically siblings and visually nothing alike, which is a good illustration of how much water in a crystal changes.
Viridian, Shade of bluish green. Wikipedia's description, not ours.
The history
Viridian arrived at exactly the right moment. Painters had emerald green, which was brilliant and lethal, and Scheele's green, which was duller and lethal, and terre verte, which was safe and weak. Viridian is bright, transparent, absolutely permanent, chemically inert and harmless, and within about thirty years the arsenic greens were gone from the artists' trade.
It became the standard green of Impressionism and after. Cézanne's landscapes lean on it heavily, and so does most late nineteenth-century painting with foliage in it. Its transparency is the key property. It glazes over a warm yellow and produces a foliage green with depth that an opaque green cannot.
It is expensive to make and is now widely substituted with phthalo green mixtures, which are stronger and cheaper and slightly different. The distinction matters in mixing: viridian is weak enough to control and phthalo is not.
Where it is used
Painting from the 1860s, cosmetics, and anywhere a stable green is needed near skin. It is one of the few greens approved for cosmetic use.
For a palette its useful quality is that it is a green with a blue bias and low saturation, which means it recedes. Almost every green a colour picker offers is a forward, saturated, slightly artificial green, and putting one in a layout usually produces the 'pharmacy' look nobody wanted. A viridian-family green does not do that, and it is the shortest route out of the problem.
Go and look at it
Cézanne's landscapes
Musée d'Orsay, Paris; Courtauld, London
Transparent green glazed over warm ground. The foliage has depth because you are seeing through the paint.
How it behaves
- Made of
- Hydrated chromium(III) oxide, Cr₂O₃·2H₂O.
- Opacity
- Transparent. It stains rather than covers, so it can be glazed over another colour.
- Lightfastness
- Permanent. It will outlive the thing it is painted on.
- Completely permanent and non-toxic, rare in this family.
- Weak tinting strength, which makes it easy to control in mixtures.
- Frequently replaced by phthalo green mixtures sold as 'viridian hue'.
The numbers
All derived from the hex, never typed beside it
- HEX
- #40826D
- What a browser and a design file want.
- RGB
- 64, 130, 109
- The same three numbers in base ten. Light, not ink.
- HSL
- 161°, 34%, 38%
- Hue, saturation, lightness, how a person describes a colour.
- CMYK
- 51, 0, 16, 49
- Arithmetic only. A real separation depends on the press, the paper and a profile.
- LAB
- 50, -26, 5
- Perceptual. L* of 50 is how light this actually looks, which HSL gets wrong.
This hex is an approximation, and a page about pigment has to say so. Viridian 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 161°
Its opposite, by the diagram
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
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
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
4.53:1 · AA
Handgloves
Black on it
4.63:1 · AA
Handgloves
It on paper
4.30:1 · Large text only
Handgloves
It on ink
4.03:1 · Large text only
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.
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