The blue that cost more than gold

For centuries, the most expensive colour on the palette was not gold: it was a blue. Ultramarine was made by grinding lapis lazuli, a stone mined only in remote Afghan mountains, which travelled 'beyond the sea' — hence the name — to reach European workshops.

At times it was worth more than gold by weight. That is why contracts of the period spelled it out in writing: how many grams, of what quality, and on which figure it could be used. It was usually reserved for the most sacred subjects, such as the Virgin's robe.

Vermeer, however, splashed it around: he even hid it under other layers of paint so the light would vibrate differently — a luxury that helps explain the debts he left when he died.

In 1826 a French chemist managed to synthesise it and the price collapsed. Today, any tube of blue contains what was once the privilege of kings.