Leonardo da Vinci on Painting

“Take a piece of glass of the size of a half sheet of royal folio paper, and fix it... between your eye and the object you wish to portray. Then move it away until your eye is two-thirds of a braccio away from the piece of glass, and fasten your head by means of an instrument in such a way as to prevent any movement of it whatsoever. Then close or cover up one eye, and with a brush or a piece of red chalk finely ground mark out on the glass what is visible beyond it; afterwards, copy it by tracing on paper from the glass, then prick it out upon paper of a better quality and paint it if you so desire, paying special attention to the aerial perspective.”

“If you wish to thoroughly accustom yourself to correct and good positions for your fingers, fasten a frame or a loom divided into squares by threads between your eye and the nude figure which you are representing, and then make the same squares upon the paper where you wish to draw the said nude but very faintly. You should then put a pellet of wax on a part of the network to serve as a mark which as you look at your model should always cover the pit of the throat, or if he should have turned his back make it cover one of the vertebrae of the neck. ...The squares you draw may be as much smaller than those of the network in proportion as you wish your figure to be less than life size...”

“When you wish to see whether the general effect of your picture corresponds with that of the object represented after nature, take a mirror and set it so that it reflects the actual thing, and then compare the reflection with your picture, and consider carefully whether the subject of the two images is in conformity with both, studying especially the mirror. The mirror ought to be taken as a guide... you see the picture made upon one plane showing things which appear in relief, and the mirror upon one plane does the same. The picture is on one single surface, and the mirror is the same. ...if you but know well how to compose your picture it will also seem a natural thing seen in a great mirror.”