Well, back to the business at hand.
It should be clear by now that I have bothered to read only three serious books on art: the Rodin, the Livingstone, and the Harold Speed. I mean, I've skimmed through some other stuff, but you're going to have to wait on me developing some discipline if you're just checking in here to find out what I have to say about Ruskin.
With the mighty armor of my ignorance in mind, let's see what Harold Speed has to say about edges. Whereas Livingstone covers the topic in terms of the empirical mechanics of the nervous system, Speed (in 1924) speculates on the origin and significance of edge-detection [p. 40]:
Sight, as the accurate perception of visual things, is a faculty that has only gradually been developed by humanity in its upward march, and few people realize how little they really see of the marvelous things happening on the retina of their eyes. Sight as a faculty is not so essential to our survival as some of our other senses, such as touch. We live more by touch than sight, and the average person uses his eyes more for the purpose of giving him information about the solidity and general felt shape of things, than for the purpose of observing the color sensations on the retina. We cannot move a yard in front of us without first knowing if there is anything solid to stand upon or something hard in front of us that we might knock ourselves against. And these are all touch ideas. But by associating touch with sight in the very early years of our bodily existence, we learn from much knocking of ourselves, and many falls, to associate sight with touch in so intimate a way that eventually the habit of seeing the touch sense in things becomes habitual; and instead of the color masses on our retina, we see an appearance of a solid world in front of us.
...how much more charming English once was, and only recently too! This concept, that sight is in its utilitarian aspect fundamentally nothing more than an aid to a touch-model of the world, is a very interesting concept. And it seems likely to me to be true, to a very large extent. Speed then uses this concept to illuminate the utilitarian origin of line in art [pp. 42-3]:
...it is only very slowly that humanity has perceived the facts of visual appearance, only gradually that we are opening our eyes, only very slowly that we have developed the faculty of sight. Each newly added fact being, as it were, a new instrument of expression added to the orchestra at the disposal of the artist. After the simple outline filled in with a little local color, we get a little shading to indicate form. And this simple formula was refined to a very high degree in the art which we call primitive, right up to the time of Botticelli...
[Then he lists some developments through 1700 A.D.]
...the whole of this growth of visual knowledge started from the outlined form, which was the result not so much of any attempt to represent what was seen as to satisfy the idea of solid things outside himself man had formed from his sense of touch. The art of the Egyptians, which is the foundation of our Western art, is obsessed by this.
To use Speed's terminology, the line is defined as serving the purpose of defining "a solid object as revealed by the sense of touch with a boundary in space." This is really fascinating! Speed contends that the representational line is not, conceptually speaking, a visual object at all! It is a visual signifier for a tactile phenomenon.
Well, that's also pretty obvious. Most visible things are touchable. But when Speed re-orders the priorities of the system of perceptions, placing touch prior to and superior to sight, he opens an avenue of evaluation of sight that is very fruitful.
To deal with simple things first, his analysis corresponds strongly with Livingstone's experimental results, which indicate that the high-resolution monochromatic edge-detection mechanism of the nervous system is very old and very much related to figuring out what's around us in space. Appreciation of the beauty of butterflies evolves later.
To get to the meat of it, Speed's analysis gives us an insight into the tremendous visceral quality that a beautiful line evokes, even though line is seen, and sight is the most outward and un-visceral of the senses. Let's look again at this Schiele picture we were studying a few days ago:
We were talking previously about the qualities of line in Schiele's work. Let's think about line again in the context of touch. When I was in high school, I had an art teacher who referred one time to "all those grotty hairs" in Schiele's nudes. What he was responding to was the tactile sense implicit in line. The hairs made his lip curl in revulsion - a visceral response - because he was imagining touching them. Take another look at that armpit hair. You can feel it. You can feel the knobs of bone in the elbow and spine. Schiele's line is expressive not only because it has a riveting and unique shape, but also because it induces a strong sense of touch. It strongly defines the quality of "a solid object as revealed by the sense of touch with a boundary in space."
Now let's get back to a Picasso portrait we also discussed before:
I'll never get tired of looking at her.
Anyhow, part of the sensuality of this portrait is that Picasso has developed a system of line that gives you a strong tactile sense of the hair. Unlike Schiele's armpits, you want to touch this hair - you want to run your fingers through it, because the line makes apparent that it is soft and voluminous. The sense of soft volume extends to the face, where the smooth curves of the cheeks reinforce the impression. Almost no shading - but a gut-level impression of volume and consistency.
I'm not particularly going anywhere with this thought, except that I wanted to add the concept of the tactility of line, as a representation of edge, to your mental catalogue as we continue to discuss edges and edge detection. I think it's important, in terms of comprehending the cognitive stakes of the inquiry, and how these cognitive stakes influence the aesthetics that we are constructing or reflecting as artists.
But I would like to add that the most sensual paintings are often the ones with the strongest implied tactility. Or, abandoning the question of touching the thing, the strongest depiction of volume, consistency, and texture of the thing-in-itself. Abandoning our topic of edges for a moment, I'd like to discuss a painting which I think of as one of the sexiest paintings I've ever run into. It was at a retrospective at the Tel Aviv Art Museum of contemporary Israeli artist Elie Shamir. It's called Miri with a Jug:
There are all sorts of reasons I think of this as a sexy painting, but we'll keep close to the topic at hand for a minute, which is the sense of a thing as a tactile thing, as having substance. So let's discuss the way that substance contributes to this painting being sexy. In this respect, there are two staggering passages, which you can appreciate better in this helpful closeup:
The first is in her right hand (our left). In that series of almost chaotic brushstrokes (the result of a painting technique the show made clear he has been refining for years), Shamir evokes blocky, strong fingers. You can tell how these fingers feel - they are mighty fingers, substantial fingers. They have a grace defined by strength. And the strength is perceived, not at the visual level, but at the tactile level.
Now you might be thinking the second passage I want to bring to your attention is her right breast (our left). Nope. It's nice, but any fool can paint a breast getting squished. It's good, but it's not unique.
No, the second passage I find remarkable is her left breast (our right). Particularly the line of slightly lighter brown extending up from the nipple to the shoulder. That line is where the flesh folds forward. Why does it fold forward? Because the mass of fat in the body of the breast is dragging down on an insufficiently robust internal system of suspensory ligaments. Or, to put it less fancily, it sags. Because the tissue cannot support it, it folds the skin, which must support it as well. This is a tremendously subtle and specific observation of the substance and consistency of the body. It is unromantic, and real, and, to me, overpowering.
So of all the reasons that I think of this painting as dazzlingly sexy, tactility is an important one. This is not some imaginary Female Nude: this is a real woman, with sturdy fingers and heavy breasts, and the tactility of her herselfness will knock you down if you let it.