The quote "Art is never finished, only abandoned", variously attributed to Leonardo da Vinci and Picasso, isn't entirely true. Sometimes you reach a point with a painting when you simply know: this is it finished. More often though, you get to a stage where you begin to wonder whether it might be, or start to worry you're going to overwork it. These tips will help you decide if it's time to down brushes or not.
If you're merely tweaking a little thing here, and another there, rather than doing something definite and decisive, then stop painting. Put the canvas aside for a while, then look at it again with fresh eyes. Sometimes you'll immediately see what you still need to do; other times you'll wonder why you thought it wasn't finished. And, yes, there will be times when you're still unsure. But if in doubt, don't tweak.
For a painting where I think it's just about done but not quite, I like to put hang it up somewhere I can see it often during the day, from different angles and distances as I go about doing other things. Not to forget the turning it upside down and the looking at it in a mirror options, both of which help you see it anew.
Are You Bored?
Fiddling and tweaking a painting also happens when you're bored with it. Nevermind why you got bored -- perhaps you've struggled too much with it, or the subject has lost its appeal. If you are, put the painting aside for now. Decide at a later date whether to continue with it or overpaint it.
If you're not working on a section of the painting because you think it's "a good bit", check it's integrated with the rest of the composition and doesn't feel like it doesn't belong. Stopping because you're too scared to change something for fear of messing it up means you'll not develop past that point. It is tough, but remember that you didn't get to that stage in the painting simply by accident, and you can get there again if you do ruin it. If you can't make yourself do it, then paint another version and take it to a further point.
Finished for Now
The painting may not be as you'd visualized it, but it may be that it's as finished as you're able to make it at this stage. Admit to yourself that it's not quite done but you don't know how -- yet. Your painting skills develop through time, as well as your style and preferences. A painting you once considered done may no longer feel like it. There's no rule you can't paint further on a canvas you once thought was finished. (See also: A Painting is Complete in Any Stage)
Check the Tones and Focal Point
Do a final check on the tones in the composition overall, and then in the focal point. Is there sufficient contrast between the lights and darks? Is the eye drawn towards the focal point? Is there an overall color unity to the composition, no stray bits of color that sit awkwardly?
Stop Sooner Rather than Later
It's far easier to add to a painting if you decide it's not yet finished than to undo something if you decide the painting didn't need it after all. You're more likely to ruin a painting by overworking it than by not finishing it.
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