It is interesting to see an artists process and progress. I painted a portrait of my husband over a few weeks. I used mostly alla prima painting techniques or wet paint into wet paint. I did let it dry between sessions. When you let oil paint dry between sittings it allows the artist to adjust the colors more easily and if you make a mistake you can wipe off your last layer! Attached you can see the progress of the painting from my initial sketch which I tried to block in the drawing and determine where my darkest darks were going to be. You can also notice that I changed the body shape a few times and adjusted the colors.