Most of my paintings thus far have been done Alla Prima, that is, in one sitting. However, I've recently taking a few classes and spent time on my own working on a painting for more then one sitting. I've discovered a few things I thought I would share.
One, I've noticed that perhaps due to lack of practice on this, I found myself getting a bit paralyzed in my thinking. I find I paint differently when I know I have lots of time, I paint with thin tentative strokes rather then jumping right in with paint and letting it go. I know when your working in multiple sessions you would like to keep your paint thin in sections you know you will be reworking on a latter day but I don't believe Mancini or Fechin worked that way. However as I am barely scratching the surface on this one I will just leave it there.
Two, there is a point in the process the paint gets a bit tacky. It is not dry or wet but somewhere in between and let me tell you, that is the worst time to work on top of an area. Your best bet is to wait until it in completely dry to tackle that area.
Three, Its difficult to keep your focus for a long period of time. Trying to visualize the end result before you begin is going to take some time and lots of canvas.
Four, Discovering what finish is in a painting can be tricky. The paintings I do spend more then one sitting on tend to look rather tight, or maybe I mean refined. Whatever it is they are not often what I intend they look like in the end, hence the visualizing what you want your painting to look like in the end. Keeping your focus and if need be I guess find a way, a skill, a technique that will teach you how to make paintings you intend to make. Not paintings that just happen
So once again, back to the easel. One brush stroke at a time.