A few years ago I asked an artist friend of mine if he used a pencil to do his initial sketch on his awesome portrait works. You'd think I had asked him if he enjoyed using dog food when making meatloaf. That guy hates the idea of using a pencil for sketching prior to painting. Comes from experience. If you use a pencil many times the pencil lines will show up through the paint....especially the lighter areas of your painting. This is the normal look when using watercolors but you don't see it so much in oil painting.
I have used pencil to do my sketching for landscape work which is fine because I hardly sketch much at all when doing landscapes. Usually the line of the mountain tops is the only problem area I have with the pencil showing through so I just scrub it lightly with the brush and it goes away. Other times I will wipe that line down with turpentine...just enough to leave just a trace of it but the paint covers it no problem. And of course, a lot of times I do the sketching with a small liner brush using a wash of turps and yellow orchre...that method works the best. The problem is I sketch a lot due to the to the detail when painting marine scenes. I can't paint a marine scene over a loose sketch. I have to have the drawing pretty exact before I paint. For a marine sketch I go back to using a pencil simply for the control I have with it. Besides....it is easier and faster to erase a pencil line than it is to go back and wipe out a line when using paint. With pencil though you have tons of line work to cover with paint. I've been thinking about maybe trying to do my initial sketch with a light grey marker pen. Tombo & Prismacolor both make markers with various greys. I'd think a 10% cool grey would probably work great for this and the oil paint should easily color this.
Some of the pencil lines still showing through in this detail shot of the painting...when the paint sets up I'll go back over them but it is tedious.
So, the next time I'm down in Pasadena I'll stop into the Blick art store and pickup a couple of these guys to try out.