The painting in the mirror
We know very well that errors are better recognized in the works of others than in our own; and that often, while reproving little faults in others, you may ignore great ones in yourself…
I say that when you paint you should have a flat mirror and often look at your work as reflected in it, when you will see it reversed, and it will appear to you like some other painter’s work, so you will be better able to judge of its faults than in any other way.
Again, it is well that you should often leave off work and take a little relaxation, because, when you come back to it you are a better judge; for sitting too close at work may greatly deceive you.
Again, it is good to retire to a distance because the work looks smaller and your eye takes in more of it at a glance and sees more easily the discords or disproportion in the limbs and colors of the objects.