The Palette/white/Dug out of the ground
Chalk
Crushed marine microfossils. Useless as a white in oil and indispensable as everything underneath it.
Also called whiting · lime white · bianco di San Giovanni · gesso
- Hex
- #EDE8DA
- RGB
- 237, 232, 218
- Pigment index
- PW18
- First used
- Prehistoric
- From
- Chalk downland: England, France, and limestone everywhere
What it is
Calcium carbonate, CaCO₃: the compressed shells of coccolithophores, which is to say plankton that died in the Cretaceous.
How it is made
Quarried, washed, levigated and dried. Lime white is a variant made from slaked lime aged in water, which is what fresco painters used and what Cennini calls bianco di San Giovanni.
As gesso it is mixed with animal glue and applied in many thin layers to a panel, then scraped and polished to an ivory-smooth surface. That surface is the reason early panel paintings look the way they do. The ground is doing half the optical work, reflecting light back through the thin paint above it.
Chalk, Chemical compound. Wikipedia's description, not ours.
The history
Chalk is the best demonstration in this whole library of why the medium matters more than the pigment does. In water-based paint (distemper, fresco, gouache) calcium carbonate is a perfectly good white. In oil it is nearly invisible. Its refractive index is too close to the oil's, so it stops scattering light and turns into a transparent filler, which is useless if what you wanted was white. Same powder. Two completely different materials, and the only variable is what it was mixed into.
Which is why it had a second career as an extender: cheap white that adds bulk without adding hiding power. That is legitimate in some products and is adulteration in others, and the line between the two is the entire history of paint regulation.
It is also the ground under most European painting before canvas took over, as gesso, and the limewash on most European buildings before modern paint. The white of a Greek island village, a Cotswold cottage interior and a Bengali courtyard are all lime, and they are all slightly different because the local stone is.
Where it is used
Gesso grounds, fresco, limewash, distemper, blackboard chalk, toothpaste, paper filling, and as an extender in almost everything.
The refractive-index lesson generalises usefully. A colour's appearance is a relationship between the pigment and what surrounds it, not a property of the pigment. That is exactly why the same hex looks different on paper, on an OLED, on an LCD in sunlight and embroidered into a polo shirt, and why a brand guideline that gives one hex and no substrates has not specified a colour at all.
Go and look at it
A gessoed panel, seen from the side
Any conservation studio, or a cross-section photograph in a catalogue
Layers of chalk and glue, polished. The ground is thicker than the painting.
The white villages of the Cyclades
Greece
Limewash, reapplied annually. A national colour maintained by a chore.
How it behaves
- Made of
- Calcium carbonate, CaCO₃: the compressed shells of coccolithophores, which is to say plankton that died in the Cretaceous.
- Opacity
- Opaque. It covers what is under it.
- Lightfastness
- Permanent. It will outlive the thing it is painted on.
- Opaque in water media, nearly transparent in oil. The medium decides.
- Dissolved by acid, so it is unsuitable anywhere acidic.
- The standard extender in cheap paint, for better and for worse.
The numbers
All derived from the hex, never typed beside it
- HEX
- #EDE8DA
- What a browser and a design file want.
- RGB
- 237, 232, 218
- The same three numbers in base ten. Light, not ink.
- HSL
- 44°, 35%, 89%
- Hue, saturation, lightness, how a person describes a colour.
- CMYK
- 0, 2, 8, 7
- Arithmetic only. A real separation depends on the press, the paper and a profile.
- LAB
- 92, -1, 7
- Perceptual. L* of 92 is how light this actually looks, which HSL gets wrong.
This hex is an approximation, and a page about pigment has to say so. Chalk 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 44°
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
1.22:1 · Fails
Handgloves
Black on it
17.16:1 · AAA
Handgloves
It on paper
1.16:1 · Fails
Handgloves
It on ink
14.94:1 · 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
Colours next to this one
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Foundations · Colour·white·Dug out of the ground