The academics solved the problem of shadow color by keeping all the shadows uniformly warm. They often painted a very warm underpainting that was preserved in the final painting. This underpinning was often burnt sienna or similar hue. If there was any modulation of the shadow color it was by very subtle glazing. This gave a similitude of reality by ensuring that the values were extremely accurate. However, color vibrancy was lost following this formula.
The revolutionary idea of the impressionists was that reality was much more complicated and could not be described using the brown formulas of the academics. Many painters began to paint in the field using direct observation to guide their color choices. Some effects were so obvious that immediately impressionist paintings began to reflect a more vibrant and colorful reality. These newly discovered methods also allowed the impressionists to pack more observation into their paintings. Instead of brown shadows we began to see the purple and blue shadows of the Impressionists. But there were even more subtleties to be discovered.
I was looking out from a twenty-four story building onto a building below. There had been a recent snow and one of the air-conditioning units on the roof was casting a long shadow. I could clearly see how the shadow was warmer closer to the air-conditioning unit and gradually cooled as the shadow lengthened. For me it adequately explained and demonstrated Monet’s envelope. This principle says that objects that protrude into the blue amorphous envelope of the sky become cooler in color. Objects or spaces that retreat from this envelope become warmer. For example, spaces and deep recesses within trees and rocks will often appear warmer than the less recessed spaces right next to them.
It’s not an easy principle to grasp. I think of it as the sky being a kind of bluish gas that wraps itself gently around every object. There are probably problems with this model and as we understand with greater clarity the natural phenomenon around us we will paint paintings with even greater vibrancy and vision. Let me know if you have any insights into this fascinating phenomenon.