The Palette/purple/Made in a lab or a works
Han purple
A synthetic barium copper silicate made in China two and a half thousand years ago, and it does something at low temperature that no other pigment does.
Also called Chinese purple · Han blue (the related compound)
- Hex
- #5218FA
- RGB
- 82, 24, 250
- First used
- c.500 BC
- From
- China
What it is
Barium copper silicate, BaCuSi₂O₆. Han blue is the related BaCuSi₄O₁₀, the same chemistry with more silica.
How it is made
Barium and copper compounds fired with silica at around 900–1000°C, probably with lead as a flux. The temperature window is even narrower than Egyptian blue's, and getting purple rather than blue depends on the ratio and the atmosphere in the kiln.
The barium is the tell. Barium is not something you stumble on; it points at a deliberate mineral choice, and one theory connects the pigment to Taoist alchemists working with barite while trying to make glass or jade substitutes. Colour as a by-product of trying to fake a gemstone.
Han purple, Pigments developed in ancient China. Wikipedia's description, not ours.
The history
Two civilisations invented a synthetic copper silicate blue independently, two and a half thousand years apart in origin and thousands of miles apart in space, and there is no good evidence of contact. Egyptian blue is calcium-based, Han blue and purple are barium-based. Either it is one of the better coincidences in materials history or there is a transmission nobody has found.
It appears on the Terracotta Army, on ritual bronzes, on beads and on painted ware, from the Warring States period through the Han dynasty. Then it disappears around 220 AD and nothing made in China after that uses it. A manufacturing capability was lost completely, which happens more often in the history of colour than people expect. Egyptian blue went the same way.
The genuinely odd part is modern. Han purple is a quantum-mechanical curiosity: cooled to a few kelvin under a strong magnetic field, its copper ions behave as a two-dimensional magnetic system and it loses a dimension, entering a Bose–Einstein condensate state. A pigment from the Warring States period is a research material in condensed-matter physics.
Where it is used
Terracotta Army figures, where traces survive on the trousers and armour of excavated warriors; bronze inlay; painted lacquer and beads. The Terracotta Army was painted and most of the paint has gone, which is worth remembering whenever you look at grey ancient sculpture.
The transferable point is the same as Egyptian blue's, and it is a business point: when a colour cannot be found, it gets manufactured, and the manufacturing capability becomes the asset. Both of these pigments were state-scale or temple-scale industrial processes, and both were lost the moment the institution funding them stopped.
Go and look at it
The Terracotta Army
Emperor Qinshihuang's Mausoleum Site Museum, Xi'an
Purple survives in patches on excavated figures. The army was fully painted, and the grey you see in photographs is loss.
How it behaves
- Made of
- Barium copper silicate, BaCuSi₂O₆. Han blue is the related BaCuSi₄O₁₀, the same chemistry with more silica.
- Opacity
- Semi-opaque. It covers, but something of the layer beneath still comes through.
- Lightfastness
- Good. Safe for anything that is not hung in direct sun for a century.
- Unstable in acid and in damp: it decomposes, which is one reason so little survives.
- Made in a very narrow firing window; blue and purple are the same recipe run slightly differently.
- Enters an unusual magnetic state near absolute zero, which is why physicists keep buying it.
The numbers
All derived from the hex, never typed beside it
- HEX
- #5218FA
- What a browser and a design file want.
- RGB
- 82, 24, 250
- The same three numbers in base ten. Light, not ink.
- HSL
- 255°, 96%, 54%
- Hue, saturation, lightness, how a person describes a colour.
- CMYK
- 67, 90, 0, 2
- Arithmetic only. A real separation depends on the press, the paper and a profile.
- LAB
- 37, 76, -98
- Perceptual. L* of 37 is how light this actually looks, which HSL gets wrong.
This hex is an approximation, and a page about pigment has to say so. Han purple 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 255°
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
7.32:1 · AAA
Handgloves
Black on it
2.87:1 · Fails
Handgloves
It on paper
6.95:1 · AA
Handgloves
It on ink
2.50:1 · Fails
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.
Watch
Titles and channels as YouTube reports them
Read more, elsewhere
Colours next to this one
Back up
Foundations · Colour·purple·Made in a lab or a works