Known from ancient times, in the Renaissance it was the standard underpainting for flesh. Fine examples from Michelangelo, Vermeer, and others.
When it was first used as a pigment, this vegetable dye proved reliable and lightfast. Later technique, though, resulting in it fading. Why?
In their original form as madder, derived from plants and poorly resistant to light. Refined to Alizarin Crimson, still fugitive, and a standard for fading. Finally fully ‘permanent’.