Norcross Station, 9 x 12 inches, oil on linen
I originally painted the Norcross Station during a workshop I taught in Atlanta last year. It was a demo, and while it wasn't a bad sketch, something about it bothered me. After I got home I tried to figure out what was wrong with it, and tried a few different solutions; lowering the value on the roof, increasing temperature shifts, emphasizing a color theme, etc.
Unfortunately I don't have an image of the original painting so I can't show you exactly what I mean, but suffice to say, it took a while for me to find a satisfactory solution, which was to essentially connect the roof shape to that of the sky, so that the roof didn't have a definitive edge all around. It had too much impact and definition before, so it took away from the signal / crossing thingy in the front left.
I didn't want the roof itself to be the main star of the painting, so it had to be subordinated somehow. Besides making the sky and the roof values very very close, I also made the background trees smaller, so more of the roof edge was touching the sky. I also made the light cooler and overcast. Which brings me to what I actually was going to talk about today.
We have to make sure a few things happen, to make a painting look like it's depicting an overcast light. We don't have the direct sunlight, for one. The entire sky becomes the primary light source, and unlike the strong directional light that the sun provides, we are dealing with a very diffused light. It's not really the function of values that makes a scene look sunny or overcast. That is to say, you don't get "sunny" by painting something lighter, and conversely, you don't necessarily get a sense of overcast by painting something darker. After all, an overcast day can feel very bright.
So how do you show diffused light? By painting your cast shadows with softer edges. This is the single biggest difference between sunny and not-sunny days. On sunny days, we have sharp(er) edges on the cast shadows, whereas on overcast days, we have soft(er) edges. This is true in any diffused light situation, whether it be overcast, hazy, foggy, dusk… The clearer the day, the sharper the cast shadow edges. In some cases the light is so diffused that we don't see any cast shadows at all.
The other thing we have to pay attention to is the temperature shift between light and shadow. In direct sun light, we often see a warm light / cool shadow relationship. Sunlight usually (but not always) feels much warmer than the shadow areas, so we mix yellows, oranges and reds in it to achieve that. We are essentially acknowledging that sunlight has color. The shadow side (on a sunny day, still) feels cooler, comparatively. Often the blue sky will make the shadows very cool and blueish, but even without the help of the blue sky, the shadow side tends to be cooler just because it's not getting the warm colored sunlight. The difference may be subtle, but it's there.
Now on an overcast day, the light feels much cooler compared to sunlight, thanks to all the clouds (condensed water vapor) filtering the sunlight. This doesn't mean you paint the lit areas blue. It just means it's cooler than if it were sunny. The shadow side is often painted warmer, but it's a pretty subtle shift most of the time. You may not even see it as shifting at all. It may just appear to be darker, but not particularly cooler or warmer.
In my painting above, the shadow is a little teeny bit warmer, due to the warm underpainting peeking through. The opaque colors I mixed for the shadows aren't noticeably warmer than the light. I didn't even try to make them warmer. I just made sure they weren't cooler.
In strong sunlight, light and shadow separate clearly, and often we amplify this separation so there's no ambiguity. This separation provides a good starting point for a solid value structure.
In overcast light, we have no such tool, so the strong value structure has to come from local values themselves. light things vs. dark things, as opposed to light and shadow providing the value structure. It makes sense, then, to look for interesting shapes in silhouettes, rather than in light / shadow patterns.
My point here is that given different light situations, you have to have an appropriate strategy to tackle the problem. If you mindlessly approach sunny days and overcast days (and foggy days and rainy days and dusk and twilight and back lit and face lit and…) the same way, your chances of pulling off a successful painting is not so great.
On the other hand, if you understand the basic characteristics of what makes a particular light situation look that way, you have an enormous head start!