Along with perspective and anatomical accuracy, the convincing depiction of skin was one of the holy grails of pictorial illusionism, the dominant criterion of successful art until the Modern era.
I drink a lot of coffee while laying in the branches, and tense up my forearm so I get a "jerkiness" in my lines.
Robert Wittig
The propensity for an art life may be tied to brain chemistry.
The observation of simple ratios of elements in body proportions and organic molecules then led to the concept of valency and valuable artworks; that seems so grotesque and silly, and ridiculous.
Jasper John's work is coded with secret messages, because he is not a purely a visual artist. With Ellsworth Kelly there is no message, just an experience.