Listen to part of a lecture in an art history class.
OK, so when we were discussing Gainsborough's painting The Blue Boy, which he painted in 1770, I mentioned the story that the painting might've been an experiment... the result of a challenge—it was believed that blue couldn't be an important color in a painting—because, well, it tends to recede into the background.
Not good for your main subject, right?
So, to show otherwise, Gainsborough created The Blue Boy, with the boy featured, large, in his famous blue clothes and, well, I guess he proved his point.
But, there was another challenge to blue—it was very, very expensive back then.
Now, of course, because of modern chemistry, any color is available in tubes at any art supply store.
But in the eighteenth century and before, it wasn't so easy.
And blue... well, the color ultramarine—the most desired shade of blue—was made from the precious stone lapis lazuli, which had to be imported all the way from Afghanistan.
And the second-most favored shade of blue... after ultramarine made from lapis lazuli... was a shade of blue that came from another precious stone, azurite.
But azurite was, well, harder to work with.
There is evidence that artists would try to get around these difficulties—for example, use pigment from lapis lazuli or azurite very sparingly and also use something cheaper, like smalt, which was made of ground glass.
Thing is, smalt became discolored over time.
So, many artists probably just avoided blues altogether, rather than use something cheap and impermanent.
So, blue, and especially ultramarine pigment, was a luxury, a status symbol—worth even more than gold at times—and you even had the wealthy ordering paintings with ultramarine to show others that they could afford something made from this precious pigment, much in the same way they'd order gold leaf.
[aside] Actually, the ancient Egyptians did manage to make an artificial blue—[impressed] the first synthetic pigment, in fact, if you can believe that!
They passed the formula on to the Greeks and Romans, but then it was lost....
[back on track] Anyway, not only was lapis lazuli hard to get, it was also hard to process.
The recipe was difficult; the stone had to be ground finely—not easy to do with a rock!—then mixed with melted wax, resins, and oils, wrapped in a cloth and kneaded, like bread dough.
The fine particles of ultramarine were then separated from the rest...
The process was time-consuming, which also contributed to the high cost of producing ultramarine, and it didn't even yield very much usable pigment.
As a result, the French government sponsored a competition in 1824 to find a cheaper way to make ultramarine pigment.
And soon after, a process was demonstrated where a combination of coal, sulphur, and other cheap, commonplace substances were heated, creating a suitable synthetic substitute for lapis lazuli.
So there's no doubt that nineteenth-century artists, after good synthetic versions were available, used more ultramarine.
Think of the Impressionists, for example... They had a lot more choices—or at least less expensive choices—than painters not that long before them...