But even here in these pieces' inchoate brushstrokes and inky splotches, borrowed imagery is lurking.
In recent years, however, the art itself has come under more scientific scrutiny, especially through the analysis of brushstrokes.
From his Chelsea flat, he would paint his view of the river, capturing boats with a few swift brushstrokes and injecting light with some expressive daubs of paint.But in the 1860s he faced an artistic crisis, explains Lee Glazer, an American art historian at the Freer.
But what it had in common everywhere was the younger generation's desire to cleanse artistic vision by painting only what they saw about them, with broad brushstrokes and brighter, simpler colours.
Francis Bacon, represented by a powerful 1965 image of a rider falling from a horse against a stark background, applied brushstrokes to canvas furiously, delighting in unpremeditated effects.
The oil sketches are full of frenetic motion, painted in dynamic brushstrokes, dripping with wind and weather, overpowered by the evocative skies he called "the chief organ of sentiment in a landscape".
For instance, when two known van Goghs, "The Plough and the Harrow" and "Wheatfield with Crows", were used for training, the system indicated that among the paintings that resembled them according to a standard measure of brushstrokes was one of the sea at Saintes-Maries, a fake commissioned or sold by Otto Wacker, a German art dealer.
Those ill-judged brushstrokes were to be Diego's downfall in America.
The dazzling colours and dashing brushstrokes of his sunflowers, cornfields and cypress trees are among the most familiar and loved works in the history of art, fetching record-breaking sums in auction rooms.
And this is when many a researcher would love to get their hands on Leonardo da Vinci's most famous muse, in order to find out more about how she was painted.For a long time, scientists and curators have wondered how da Vinci created shadows on her face with seemingly no brushstrokes or contours.
"They're dismissed for what they are," says one official at the Texas Land Office: "federal, socialist, environmentalist plots".Yet the broad brushstrokes of land-ownership are clear.
