The Palette/blue/Ground from a rock or crystal

Azurite

The blue most old paintings are actually made of, because it was the one a normal person could afford.

Also called mountain blue · azzurro della magna · bice

Hex: #2C6BA0
RGB: 44, 107, 160
Pigment index: PB30
First used: Ancient Egypt onward; the standard European blue c.1400–1700
From: Copper deposits: Hungary, Germany, Spain, China, Sinai

What it is

Basic copper carbonate, Cu₃(CO₃)₂(OH)₂. The same chemistry as malachite with less water in it, which is why the two are found side by side.

How it is made

Hand-sorted from copper ore, then crushed and washed. Unlike lapis it does not need the resin-dough extraction, because the blue mineral is already most of the rock, but it does need careful sorting, since azurite and green malachite grow in the same deposits and often in the same lump.

Grinding is the danger. Azurite loses colour as it gets finer: coarse particles are a strong deep blue, fine ones go pale and sickly. So it is ground as little as possible and the paint stays gritty, which forces a particular kind of brushwork: thick, opaque, laid on rather than blended.

Azurite, Copper carbonate mineral. Wikipedia's description, not ours.

The history

If you are looking at a European painting made before about 1700 and the blue is not the Virgin's best robe, it is probably azurite. It was available, it was affordable, and Cennini and every other handbook treats it as the working blue and ultramarine as the luxury.

Its reputation suffered from one fault: over centuries, in the presence of damp, azurite can alter towards green. A number of paintings whose skies and foliage now look wrong were not painted that way, the blue turned. This is worth knowing when you look at early panels and think the colour judgement is strange. Sometimes the colour judgement was fine and the chemistry moved.

In China the same mineral was the standard blue for centuries and was used with a much finer sense of graduation than European practice: laid in thin washes rather than thick opaque passages, which is the other way to handle a pigment that fails when ground small.

Where it is used

Almost all pre-1700 European blue that is not ultramarine: skies, drapery, the blue-green of distance. Also Chinese and Japanese painting, Persian and Mughal manuscripts, and Egyptian work long before either.

The lesson for a palette today is about honest hierarchy. Old studios ran two blues on purpose: an expensive one placed where it would be read as a decision, and a cheap one doing the volume. Most brand palettes pretend every colour is equally precious. Deciding which of your colours is the ultramarine and which is the azurite is a more useful exercise than adding a fourth.

Go and look at it

Mughal miniature painting
Victoria and Albert Museum, London; Chester Beatty, Dublin
Mineral blues laid in flat, burnished fields. The V&A's masterclass below shows the stone being ground for exactly this.
Early Netherlandish panels with green-ish skies
Most European collections
Often azurite that has altered. The painter's intention was blue.

How it behaves

Made of: Basic copper carbonate, Cu₃(CO₃)₂(OH)₂. The same chemistry as malachite with less water in it, which is why the two are found side by side.
Opacity: Opaque. It covers what is under it.
Lightfastness: Good. Safe for anything that is not hung in direct sun for a century.

Can alter to green over centuries in damp conditions, a real cause of paintings that look mis-coloured.
Loses saturation the finer it is ground, so it is used coarse and gritty.
Incompatible with acidic mediums, like most carbonates.

The numbers

All derived from the hex, never typed beside it

HEX: #2C6BA0; What a browser and a design file want.
RGB: 44, 107, 160; The same three numbers in base ten. Light, not ink.
HSL: 207°, 57%, 40%; Hue, saturation, lightness, how a person describes a colour.
CMYK: 72, 33, 0, 37; Arithmetic only. A real separation depends on the press, the paper and a profile.
LAB: 44, -2, -34; Perceptual. L* of 44 is how light this actually looks, which HSL gets wrong.

This hex is an approximation, and a page about pigment has to say so. Azurite 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 207°

Its opposite, by the diagram

#2C6BA0

#A0612C

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

#2C6BA0

#4C81AE

#6B97BD

#96B5D0

#C0D3E3

#DFE9F1

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

#2C6BA0

#255B88

#1F4B70

#163650

#0D2030

#071018

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
5.65:1 · AA

Handgloves

Black on it
3.72:1 · Large text only

Handgloves

It on paper
5.36:1 · AA

Handgloves

It on ink
3.24:1 · 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.