The book What Painting Is, by James Elkins, examines the actual process of creating an image by putting paint ("Water and stones") on canvas. He compares this endeavor to the ancient practice of alchemy, which (like painting) involves experimenting with materials in an open-ended way. The text, which is more about alchemy than painting, becomes very dense and obscure in the later chapters, but the first chapter has a beautiful description of what happened when one of his students (he teaches at the Art Institute of Chicago) studied a Monet painting by trying to copy it in a museum.
"An ordinary square inch in a Monet painting is a chaos, a scruffy mess of shapeless glints and tangles. His marks are so irregular, and so varied, and there are so many of them, that it is commonly impossible to tell how the surface was laid down."
His student nearly gave up in frustration. In her paintings, both the texture and the brushmarks appeared too uniform compared to the original Monet. For months, they kept trying, studying and trying again. Eventually, they discovered two important things.
"First, it is necessary to have paint at the exact right texture. As it comes from the tube, oil paint is too thick, but if it is thinned with even a little turpentine, it is too dilute."
Eventually, his student used a combination of oils and varnishes to create the desired consistency, which could be smeared, scumbled, scraped and swiveled in unexpected ways. This was the second factor: the combination of delicacy and violence in the impulsive brushmarks. There was no pattern in their direction, thickness or gesture. Everything was "deliberately a little out-of-control." This process is completely empirical and intuitive. It isn't the kind of thing that one can teach in an art class.
"The state of mind that can produce those unexpected marks is one divided against itself: part wants to make harmonious repetitive easy marks, and the other wants to be unpredictable."
The comparison of painting and alchemy is sound: a combination of focus and experimentation with "water and stones" in order to create something new, which in turn changes our awareness.