As I have already said, only personal experience can teach you the smaller but not less important details in the laying of your grounds. It requires both nicety and practice to find out the exact proportion of medium (whether oil or egg) required to hold your colour properly. How to get your work to withstand, as it ought to do, either sun or damp, is only learnt by making experiments. Get different sorts of canvas, and nail pieces on to a large board; prepare these in different ways, and when the grounds are perfectly dry paint anything you please on them. The simpler tints used the better. Set them out in the open air, in wind, sun, and rain, until you find what will stand. You may be quite sure that if they stand these atmospheric changes time will not alter them. I put my largest pictures out of doors in all stages of painting, as well as after they are finished, in the hottest sun of summer, or the cold of winter, and do not find them affected by it, but this result was not attained until I had bought my experience, my first attempt occasionally cracking and peeling off.,