But what about the medieval artist who wanted a brilliant blue but didn’t have deep pockets.

Ultramarine was far too dear for any but the smallest or choicest works, Azurite was by no means cheap, indigo and woad were not bright enough for all purposes.

There was however another choice: Blue Verditer, which was probably more signi cant in medieval painting than all the other blues put together. It is certain that for every kilo of ultramarine used in the medieval painting, many tonnes of copper blues were used.

It is a synthetically manufactured azure blue pigment, prepared by the reaction of a copper sulfate with calcium carbonate. This basic copper carbonate was rst made in the Middle Ages and continued to be widely used up to the 19th century for panel painting, distemper and oil based interior house paints. Blue verditer particles are more rounded and regular in size than ground azurite to which it is chemically related.

Also known as blue bice and blue ashes, it is no longer commonly used and the making of this once-famous colour is now almost extinct.

The sample for the exhibition is manufactured in England by Keith Edwards, the last great colourmaker of this pigment.