The Palette/yellow/Ground from a rock or crystal
Orpiment
A brilliant golden yellow that is arsenic sulfide, was believed to contain actual gold, and cannot be used next to lead or copper without destroying both.
Also called King's yellow · auripigmentum · hartal · zarnikh
- Hex
- #EFC81A
- RGB
- 239, 200, 26
- First used
- Ancient Egypt and Mesopotamia onward
- From
- Persia, Anatolia, China, and volcanic deposits generally
What it is
Arsenic trisulfide, As₂S₃.
How it is made
Mined as a soft golden mineral, hand-sorted and ground. It cleaves into golden flakes that look convincingly metallic, which is why the Latin name auripigmentum means 'gold pigment' and why alchemists spent centuries trying to get gold out of it. There is no gold in it.
A synthetic version, King's yellow, was made by combining arsenic and sulfur. It was brighter, more uniform and considerably more dangerous to manufacture.
Grinding it is a genuinely bad idea and always was. Craft manuals from several traditions warn against it in terms that make the reason obvious, and the standard advice (grind wet, keep it away from your face, wash) is the same advice a modern safety sheet gives.
Orpiment, Orange-yellow arsenic sulfide mineral. Wikipedia's description, not ours.
The history
Orpiment was the best bright yellow available for most of recorded history, and it was used everywhere: Egyptian coffins, Mesopotamian and Persian work, Chinese and Central Asian painting, Indian manuscripts, Byzantine and European illumination. Hartal is still sold in Indian bazaars.
It has two crippling incompatibilities. Put it next to lead white or red lead and the sulfur and lead react, both pigments blacken. Put it next to a copper green like verdigris and the same thing happens. So a painter using orpiment had to plan the whole picture around it, keeping it physically separated from half the palette, and plenty of medieval manuscripts have black smears where somebody did not.
It was also an actual poison in wide use, as a depilatory, a fly killer, a medicine and a murder weapon. Arsenic's reputation as the classic poison of the Renaissance is not separable from the fact that it was sitting in every painter's and apothecary's cupboard as a yellow powder.
Where it is used
Manuscript illumination, panel painting, Egyptian and Persian work, and Indian and Central Asian painting. Replaced by chrome yellow and then cadmium yellow in the nineteenth century, which nobody mourned.
There is one genuinely useful idea in it: some colours cannot be next to other colours for material reasons, not aesthetic ones. That is still true, in a different form. A fluorescent ink will not survive UV varnish. A metallic will not overprint. A Pantone will not reproduce in process. Half of what looks like conservatism in a printer's advice is this kind of incompatibility, and it is worth asking which it is rather than arguing.
Go and look at it
Egyptian painted coffins
British Museum, London; Egyptian Museum, Cairo
The golden yellow that is not gold leaf. Often alongside Egyptian blue.
Illuminated manuscripts with blackened passages
Any major manuscript collection
Where orpiment met lead white. The damage is the evidence.
How it behaves
- Made of
- Arsenic trisulfide, As₂S₃.
- 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
Arsenic trisulfide. Poisonous by ingestion and inhalation. The dust is the danger.
- Blackens lead and copper pigments on contact, a real planning constraint.
- Degrades in light and damp to a white arsenic compound.
- Cleaves into golden flakes, which is why it was mistaken for a gold ore.
The numbers
All derived from the hex, never typed beside it
- HEX
- #EFC81A
- What a browser and a design file want.
- RGB
- 239, 200, 26
- The same three numbers in base ten. Light, not ink.
- HSL
- 49°, 87%, 52%
- Hue, saturation, lightness, how a person describes a colour.
- CMYK
- 0, 16, 89, 6
- Arithmetic only. A real separation depends on the press, the paper and a profile.
- LAB
- 82, -1, 80
- Perceptual. L* of 82 is how light this actually looks, which HSL gets wrong.
This hex is an approximation, and a page about pigment has to say so. Orpiment 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 49°
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
1.62:1 · Fails
Handgloves
Black on it
12.95:1 · AAA
Handgloves
It on paper
1.54:1 · Fails
Handgloves
It on ink
11.27:1 · 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.
Read more, elsewhere
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Foundations · Colour·yellow·Ground from a rock or crystal