First, you must be told that the canvas must be good, strong, smooth, and well made; that it must be prepared with a thin ground, and must be so durable as to last as long as the picture, and it is the duty of he who buys the canvas to ascertain this, for if the canvas is bad it decays in a short time. Smooth canvas requires but little ground for priming, for if the priming be too thick, the colours become black from the abundance of oil which is used, and the repetition of so many primings; wherefore you must take good canvas, stretch it on the frame, and give it a coat of glue made of the parings of very young pigs' skins, that it may be softer, for such glues as parchment glue, being strong and harsh, cause a certain shrinking of the canvas, which has a bad effect, therefore do as I teach you.,When this coat is dry, polish it with pumice stone, give it another coat of glue, as before, and let it neither be too weak nor too strong; for if too weak it will cause the colour to crack; that which is the proper consistence will be soft like jelly when it is cooled.,