Azurite was the primary blue pigment in European painting from the 13th to 17th centuries — the alternative to ultramarine for painters who could not afford lapis lazuli. It was mined in France, Germany, and Hungary and sold through intermediaries across Europe. Its gradual conversion to green malachite explains the distinctive green passages in many medieval paintings that were originally blue.

Rich, mineral, and slightly unstable. Azurite carries the tension of a beautiful colour that transforms over time — the blues in medieval paintings were once more vivid, and we see them now through the lens of centuries of slow chemical change. It is a colour with a built-in mortality.

The conversion of azurite to malachite in medieval paintings has dramatically changed our visual experience of Gothic and early Renaissance art. The blue sky in many medieval Madonnas is now green — the original vivid azure blue has converted over 500 years. Conservation scientists use X-ray fluorescence and infrared reflectography to identify azurite that has greened, allowing reconstruction of original colour intentions.