Above you can see the demonstration painting I began in class. I used PanPastels on a piece of white Pastelmat paper 18" x 9" in size. I'd say there's about a half-hour to an hour of work in it up to this point. It needs to be finished, of course.
First of all, in class we discussed some of the key points about painting a large open space. To review, we identified the four values of the landscape. Do you know these? They are light, medium-light, medium-dark and dark. That is: sky, ground plane, mountains and trees. It's a generalization that doesn't work in all cases, but is true often enough to be quite useful. Things become a rule because as a rule they are so. (See chapter three, 'Angles and Consequent Values', in John F. Carlson's Carlson's Guide to Landscape Painting (1929), for more information on this.)
There are five rules of aerial perspective that landscape painters use all the time. As the eye looks into the distance: Colors become cooler. Colors become less intense. Detail is lost, edges soften, and value contrasts diminish.
I have yet to establish the detail in the fore-to-middle ground in the demo painting above, but the color is already starting to work. Notice how the yellow-green grass becomes much bluer in the distance. Likewise the more distant mountains have less purple. There's a reason for that, another set of rules that, as a rule, work: In the foreground you see all the mixtures or red-yellow-blue. In the middle ground the yellow is filtered out leaving purples (mixtures of red and blue.) In the distance red is filtered out, leaving blue. The atmosphere is basically a big blue filter. Leonardo observed and recorded this phenomenon. He said: "Thus if it is to be five times as distant, make it five times bluer."
So at it's most basic level you could reduce the landscape to three colors, like this:
The box on the left side looks harmonious and correct to me, while the box on the right feels upside down and unbalanced. That's because the blue filter usually causes us to see the landscape the way it is on the right: yellow foreground, purple mountains, blue sky.
In his book John Carlson states the law of aerial perspective: "All colors become cooler in color and lighter in value as they recede from the eye, except white." Why is white an exception? Because technically it's a value, not a color! White becomes slightly duller and often shifts to rose or yellow at great distance, becoming pure white as it nears you. But the rest of the colors in the landscape are progressively filtered to become more and more blue, and lighter and lighter in value.
Here in New Mexico, where I live and teach, we have to take into consideration altitude and humidity, as well. We have plenty of altitude, rising from 5,000 ft. to over 14,000 ft. in the highest mountains, but we have almost no humidity. At altitude the air is literally thinner than it is in lower regions. The lack of moisture means we have clear air that allows us to see details a hundred miles away! If you're painting on the beach, you need to take the reverse into consideration--more air, more vapor, less detail much sooner. But there are days when I can see the crisp edge of a mountain I know is 50 miles distant--it looks like its across the street. To paint believably here, edges stay tight and crips much longer than they do elsewhere, something you have to consider when viewing someone else's artwork.
I found a wonderful illustration that might interest those working on still life, portrait or other genres of painting. It's self explanatory: Atmospheric Perspective. The visual alone is worth looking at. Test yourself before you read it and see if you can identify the nine recession cues mentioned there. (Hint: some are mention in the five rules above.) These cues can help you create the illusion of air between the nose and ear in a portrait, or between the apple and the copper pot behind it in a still life.
Keep going, gang!