The Palette/yellow/Made in a lab or a works
Chrome yellow
The loudest yellow of the nineteenth century, the colour of Van Gogh's sunflowers, and it is going brown while you watch.
Also called lead chromate · school-bus yellow
- Hex
- #FFB300
- RGB
- 255, 179, 0
- Pigment index
- PY34
- First used
- 1809, commercially from the 1810s
- From
- Paris
What it is
Lead chromate, PbCrO₄, sometimes with lead sulfate to shift the hue paler.
How it is made
A soluble lead salt and a chromate solution are mixed and the yellow precipitates immediately. Cheap, fast and easy. Louis Nicolas Vauquelin identified chromium in 1797 and described the pigment in 1809; once chromium ore supplies opened up it became one of the cheapest bright pigments ever made.
Adding lead sulfate during precipitation gives the pale 'lemon' versions. Mixing with Prussian blue gives chrome green, which was sold by the ton and is the green of a great deal of Victorian paintwork.
The history
Chrome yellow is the first cheap brilliant yellow in history, and it went everywhere within twenty years: paint, coachwork, printing, wallpaper, toys. American school buses are the colour they are because of a 1939 standardisation on a chrome-yellow shade chosen for visibility at dawn and dusk, and that colour outlived the pigment.
Van Gogh loved it and used several grades of it, heavily, in the Sunflowers and the Yellow House and the wheatfields. It is also degrading: lead chromate reduces to a brown-green chromium(III) compound under light, particularly the paler sulfate-containing versions, and synchrotron studies at Antwerp and Delft have mapped the change in his paintings directly. The Sunflowers are browning, it is not reversible, and it is the reason those works travel less and less.
It has a long industrial tail. Road markings, safety yellow and printing inks used it for most of the twentieth century, and lead chromate has been restricted progressively since, which is why yellow road paint changed shade in living memory.
Where it is used
Nineteenth and twentieth-century painting, coach and industrial paint, road markings, printing ink, and safety signage before the cadmium and organic replacements.
For a designer the Van Gogh case is the best available argument for specifying materials rather than appearances. He chose a colour; he got a chemical reaction with a half-life. Anything you make that has to last (a sign, a shopfront, a printed edition, a facade) is a materials decision pretending to be a colour decision, and the material is what will be there in thirty years.
Go and look at it
Sunflowers
National Gallery, London; Van Gogh Museum, Amsterdam; Neue Pinakothek, Munich
Compare two versions in two collections. They are diverging, and the chemistry is why.
The catalogue recordAn American school bus
Any American road
National School Bus Glossy Yellow, standardised in 1939 on a chrome-yellow shade. The name outlived the pigment.
How it behaves
- Made of
- Lead chromate, PbCrO₄, sometimes with lead sulfate to shift the hue paler.
- Opacity
- Opaque. It covers what is under it.
- Lightfastness
- Moderate. It will move, noticeably, within decades, faster in thin films and tints.
Hazard
Lead chromate. Both lead and hexavalent chromium, toxic and carcinogenic. Heavily restricted.
- Darkens to brown-green under light. Van Gogh's yellows are actively degrading.
- Blackens on contact with sulfur compounds.
- The paler 'lemon' grades degrade fastest, because of the lead sulfate in them.
The numbers
All derived from the hex, never typed beside it
- HEX
- #FFB300
- What a browser and a design file want.
- RGB
- 255, 179, 0
- The same three numbers in base ten. Light, not ink.
- HSL
- 42°, 100%, 50%
- Hue, saturation, lightness, how a person describes a colour.
- CMYK
- 0, 30, 100, 0
- Arithmetic only. A real separation depends on the press, the paper and a profile.
- LAB
- 78, 17, 81
- Perceptual. L* of 78 is how light this actually looks, which HSL gets wrong.
This hex is an approximation, and a page about pigment has to say so. Chrome yellow 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 42°
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
1.79:1 · Fails
Handgloves
Black on it
11.70:1 · AAA
Handgloves
It on paper
1.70:1 · Fails
Handgloves
It on ink
10.19:1 · 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.
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Foundations · Colour·yellow·Made in a lab or a works