Rennaissance paintings of the Virgin Mary, for which ultramarine blue was the traditional expensive pigment, are as vivid today as when they were painted five c

Rennaissance paintings of the Virgin Mary, for which ultramarine blue was the traditional expensive pigment, are as vivid today as when they were painted five centuries ago. Mineral pigments like ultramarine (i.e., finely ground lapis lazuli) are essentially perfectly lightfast. Cobalt blue is a metal rather than a silicate but still considered gold standard lightfast where artists are concerned: Chinese pottery has used it for millenia and shown no tendency to change hue. Cobalt blue is toxic but ultramarine isn't. It's possible that YinMn is similarly lightfast, but the historical blues remain cheaper and more than lightfast enough for virtually any artist concerned with longevity.