One from the archives, but had to include it. This was done plein aire on a beautiful fall day I went to Eleven Mile Canyon with a pastel painting friend. I didn't have any white oil paint with me for mixing colors. (Somehow I had neglected to replace the used tube from the previous trip.) I was stuck, as we were a long way from home. I painted it anyway, oil on canvas, and simply wiped back to the white canvas and thinned layers of oil I didn't want as dark as the colors I'd mixed. It worked surprisingly well, kind of like sculpting out the painting. I have used this technique since then on purpose.