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She dug a narrow, shallow, 41-foot-long trench in the ground, running perpendicular to the Pacific Ocean, and poured powdered ultramarine pigment into it.

International Klein Blue, or I.K.B. for short, is a combination of ultramarine pigment and a chemist’s polymer binder that keeps it from fading.

Whether ultramarine, cerulean, Egyptian or cobalt, blue pigments have colored artworks for centuries.

With the alley closed to the public, he strode into the room like the boy-mayor of the place, resplendent in an ultramarine bowling shirt.

The beddejak in “Woman in Blue Reading a Letter,” Martine tells me, is painted with ultramarine, the rarest and most expensive of the blue pigments that would have been available to a 17th-century Dutch painter.