Behaviour of azurite and malachite applied on a support of fresh lime mortar. At left, state of pigments when applied. At right, state after twelve hours. The test shows that azurite (upper band) and malachite (lower band) degradate in contact with fresh lime. The blue color of the azurite becomes pale and greyish, and the green of the malachite changes to dark greyish brown. The presence of unchanged azurite and malachite pigments in Roman wall paintings indicate that the painting was not done on a fresh lime mortar, but on a dried one.