I don't draw, paint or sketch, but I do sculptures. In the art club I am in there are a few talented artists. A couple of them do landscapes. When out with them, it is not unusual for them to stop and sketch. I have noticed that they use small sketchpads for this. They do a rough outline of the horizon, then fill in the foreground. Colours are not added but they make notes about the view.
While they are doing this, I go and collect rocks to carve.
Now does anyone know how to make a rock weigh less?