The Beauty and the Fading of Ultramarine

In his book Bright Earth: Art and the Invention of Color (public library), Philip Ball dedicates two chapters to specific colors, purple and blue.  In the chapter on blue, entitled "Shades of Midnight: The Problem of Blue," he discusses the striking shade of ultramarine:
It is inconceivable that the cost and effort involved in making ultramarine would have been tolerated if the result had not been so beautiful.  Its hue marks the transition from dusk to night, with a purple tint to enhance its majesty.  Cennino sings its praises rhapsodically: "Ultramarine blue is a color illustrious, beautiful, and most perfect, beyond all other colors; one could not say anything about it, or do anything with it, that its quality would not still surpass" (238).
Ultramarine pigment - Credit: PD

Toward the end of his book, in chapter eleven entitled "Time as Painter: The Ever-Changing Canvas," Ball also explains that understanding how a painting will age is key:
Any major gallery must have a team of dedicated conservators if its collection is not to fall quickly into a sorry state.  The technical reports produced by these teams make sobering reading.  Here you might encounter your favorite pictures . . . in a barely recognizable form before the conservators got to work on them.  Soon enough you are prowling the galleries with a suspicious eye, asking yourself: Is this a before or an after?  Should these skies really be so washed-out, these greens really so murky?  Many changes are, sadly, irreversible, yet an ability to recognize them allows one to reevaluate the picture, to sense what beauty must have been present before this ultramarine went black, before that red lake faded.  You will soon begin to appreciate that no critical analysis of paintings should be undertaken without a sound knowledge of how colors age (252).