If you paint regularly, you know the "zone". This can be the "zone" where a painting is coming together beautifully and you are loving every every painting moment. Most of the time, however, stepping away from the "wonderful" painting that was in your mind's eye allows you to see that what you are painting just isn't "doing it". This is illustrated top left. My intention was to paint an orange slice that glowed from the backlighting. I worked and reworked the glowing shadows until they were muddy ("Muddy" is often a result of the wrong color temperature). I wondered whether the background was the problem. I took a paper towel soaked in gamsol and wiped back the background. Note that this painting was left for almost 24 hours and it was still pretty easy to wipe the painting back. Without the background, the little orange slice still didn't have the glow I wanted. I believe the problems causing this included color transitions that were not small enough (yellow to yellow orange to orange to red orange) and none of the transitions moved into greyed/neutralized oranges.
I wiped the rest of the canvas.
I had to check my helper's head to see whether she was also "gamsol ed" as she bumped about under the board.