When you are painting you should take a flat mirror and often look at your work within it, and it will then be seen in reverse, and will appear to be by the hand of some other master, and you will be better able to judge of its faults than in any other way.
Leonardo da VinciYou don't get into trouble because of the things you don't know. It is the things you don't know you don't know that really get you into a mess.
Leonardo da VinciIn fact, whatever exists in the universe, in essence, in appearance, in the imagination, the painter has first in his mind and then in his hands ... it lies in his power to create them . . .
Leonardo da Vinci