On Describing a Painting

Harvard art historian bills her article thus: The Power of Patience: Teaching students the value of deceleration and immersive attention. OK. But I take a different lesson from it, one about one of my current hobby horses: description. Roberts focuses on an 18th Century painting by John Singleton Copley, A Boy with a Flying Squirrel. Her point is that the more you look at the painting, the more you notice and hence the more you can note in a written description. She asks her students to spend a full three hours with a single painting.
Of her own experience with that painting she observes:

It took me nine minutes to notice that the shape of the boy’s ear precisely echoes that of the ruff along the squirrel’s belly—and that Copley was making some kind of connection between the animal and the human body and the sensory capacities of each. It was 21 minutes before I registered the fact that the fingers holding the chain exactly span the diameter of the water glass beneath them. It took a good 45 minutes before I realized that the seemingly random folds and wrinkles in the background curtain are actually perfect copies of the shapes of the boy’s ear and eye, as if Copley had imagined those sensory organs distributing or imprinting themselves on the surface behind him. And so on.

She begins her next paragraphL "What this exercise shows students is that just because you have looked at something doesn’t mean that you have seen it." Just so. And just because you've read a literary text, or seen a movie doesn't mean that you know, in any precise and focused way, what's in it.
She tells us something about the (rather interesting) origins of the painting and goes on to make a number of art historical points about the painting:

We can see this directly in the painting, which is full of allusions to time, distance, and patience. The painting is about its own patient passage through time and space. Look at that squirrel. As the strange shape of the belly fur indicates, if one takes time to notice it, this is not just any squirrel but a flying squirrel, a species native to North America with obvious thematic resonances for the theme of travel and movement. (The work’s full title is A Boy with a Flying Squirrel.) Moreover, squirrels in painting and literature were commonly understood to be emblems of diligence and patience. Then: the glass of water and the hand. Across his long career, this is the only glass of water that Copley ever included in a painting. Why? Well, for one thing, this motif evokes the passage of a sensory chain across a body of water and thereby presents in microcosm the plight or task of the painting itself. Or think about the profile format of the portrait—unusual for Copley. It turns out that in the eighteenth century, the profile format was very strongly associated with persistence in time and space. Where was one most likely to see a profile? On a coin. What is a coin? In essence, a coin is a tool for transmitting value through space and time in the most stable possible way. Coins are technologies for spanning time and distance, and Copley borrows from these associations for a painting that attempts to do the same thing.

Obviously, you have to note those things in the painting before you can make the contextual links. At the same time contextual knowledge sensitizes you to what's in the painting (the so-called hermeneutic circle).
Paintings, like literary texts or movies, are very complex objects, with many properties. It is through description that some among those properties enter into the intellectual record for further notice and discussion.