Oil painting wet on wet provides opportunities that fast drying acrylic cannot serve. Even when dividing up a painting into sections or passages it is rare that an area can be completed. So it is necessary to work one edge against another. This requires some finesse with your brushwork – don’t skimp on brush quality. You will want to drag a good line against an existing field of paint. A good brush with long enough bristles will help to get a clean line flowing along the edge. Thin the paint to the point where it is flowing but the pigment is not diluted to be transparent. The hue and color should be intact but it should flow nicely off the edge of the brush. Regular paint thinner or linseed oil thinned with paint thinner works though I now prefer Gamblin’s Galkyd SLow Dry. Turpentine works as well.
About a 1/2 inch away bring your loaded brush up close to the adjacent field of paint previously painted and carefully begin to drag a bead along that edge. It will take some practice to load up the brush just enough to cut a line and not leave a bead of paint along the edge. If done this way the two colors will not intermix and you will have a good line between the two colors. An entire painting can be processed this way. You don’t have to wait for one field to dry before painting other adjacent areas.
Painting wet on wet, or wet against wet (to be more accurate) allows you to keep painting while the inspiration is still there. I paint very free abstracts but also some tight geometrics where precise color hue is placed against its neighbor. This method of loading the brush so that it flows with a medium but still retains its hue allows me to keep painting for a longer period. The next day it is still pliable to continue working. It is always adviseable for beginners to have a spare canvas handy and try dragging the brush to see how sharp a line you can cut before going to your actual piece. One last tip – if you happen to sneeze and you pigment goes over into the adjacent color, you can always later go back to your pallete, find that color and straighten it out from the other side. By the way it is standard practice to balance your stroke by resting the small finger against the canvas. This will help keep your line steady,