Clouds are objects with volume, obeying the rules of perspective.
|Whiteface makes its own weather, by Carol L. Douglas|
Clouds are not flat. The same perspective rules that apply to objects on the ground also apply to objects in the air. We are sometimes misled about that because clouds that appear to be almost overhead are, in fact, a long distance away.
I’ve alluded before to two-point perspective. I’ve never gotten too specific because it’s a great theoretical concept but a lousy way to draw. Today I’ll explain it.
A two-point perspective grid. You don't need to draw all those rays, just the horizon line and the two vanishing points.
A cube drawn with perspective rays. It's that simple.
|All objects can be rendered from that basic cube.|
I've included a simple landscape perspective here, omitting some of the backside lines for the sake of clarity. (I apologize for the computer drawing; I’m recovering from surgery and it’s hard to draw with my foot up.)
As a practical tool, two-point perspective breaks down quickly. In reality, those vanishing points are infinitely distant from you. But it’s hard to align a ruler to an infinitely-distant point, so we draw finite points at the edges of our paper. They throw the whole drawing into a fake exaggeration of perspective. That’s why I started with a grid where the vanishing points were off the paper. It doesn’t fix the problem, but it makes it less obvious.
Staircase in two-point perspective, 1995, Luciano Testoni.
The example above is from Wikipedia’s article on perspective. It’s a masterful drawing, but it isn’t true two-point perspective, because he tosses in several additional points. There is also three-point perspective, which gives us an ant’s view of things, and four-point perspective, which gives a fish-eye distortion reminiscent of mid-century comic book art. And there are even more complex perspective schemes. At that point, you've left fine art and entered technical drawing.
Still, two-point perspective is useful for understanding clouds. Clouds follow the rules of perspective, being smaller, flatter and less distinct the farther they are from the viewer. The difference is that the vanishing point is at the bottom of the object, rather than the top as it is with terrestrial objects.
|Basic shapes of clouds using the same perspective grid.|
Cumulus clouds have flat bases and fluffy tops, and they tend to run in patterns across the sky. I’ve rendered them as slabs, using the same basic perspective rules as I would for a house. If I wasn't elevating my foot, I'd have finished this by twisting and changing their shapes in my imaginary bounding boxes.
|Mackerel sky forming over the Hudson, by Carol L. Douglas|
A flight of cumulus clouds or a mackerel sky will be at a consistent altitude. That means their bottoms are on the same plane. However, there can be more than one cloud formation mucking around up there. That’s particularly true where there’s a big, scenic object like the ocean or a mountain in your vista. These have a way of interfering with the orderly patterns of clouds.
I don’t expect you to go outside and draw clouds using a perspective grid. This is for experimenting at home before you go outside. Then you’ll be more likely to see clouds marching across the sky in volume, rather than as puffy white shapes pasted on the surface of your painting.