When you come to paint your picture on the tempera ground (method No.2), you must be very careful that the oil mixed with your colours penetrates through the ground to the canvas. If the ground be prepared on a raw canvas there is generally no difficulty about this; but it once happened to me, when I was painting over a tempera ground with very thin oil colour, that there was not sufficient oil in the colour to penetrate to the canvas.,The result was, that on putting it out of doors, the damp penetrated into the preparation, and it all peeled off on the slightest friction. Satisfy yourself, then, that in the oil painting the oil penetrates through the ground to the canvas. If it fails to do this in your first painting, you must go over the whole of it again with rather thicker oil colour.,