Warehouses and Old Tracks 5x7 oil on c.b.
I think the worst thing that can happen to a plein air painter while he is working is changing light from cloud cover. i can take winds up to 40 mph blowing my easel and umbrella around. bums trying to get wine money while i'm scanning values is fine. bugs crawling up my leg in high weeds still ok. but let a cloud get in front of the sun or some milky clouds take over a once clear sky and you have to really earn your money!
what happens is the shadows all disappear and all the colors change. quite simply- you are no longer looking at the same scene.
that is exactly what happened while painting this. when i started the sky was milky from high clouds that were partially hiding the sun. so i lay down the underpainting with the sky being the lightest value and the rest middle values with a few dark areas under overhangs, telephone poles, etc. i'm painting away and then boooom the sun pops out- the sky looks deep blue and the walls of the warehouses went full on orange.
the thing to do (which is hard) is to ignore the sunny scenario if you started with the slightly overcast one. if you start changing midstream, you are- whats called- 'chasing the light'. all your values will be mixed up and you'll have a mess.
so stick with one value plan even if it changes before your eyes as the painting progresses. good memory for the original scene and painting what caught your eye in the first place will keep the painting from ruin.
if you'd like more explanation on value plans leave a comment below