“High lights and shadows are those painted lines in scenery hat give the effect of thickness and perspective. Well done, they do just that, but ill done, they merely confuse and make the setting messy. Unless you have an eye for color and have learned to line, better by far to forget the high lights and shadows on your set.
For lining, practice makes perfect. You need some lining brushes – a special scenic brush with long bristles and handles – and a straight edge. Hold the straight edge in your left hand in such a manner that the top edge of the stick is unobstructed by your fingers, to allow for free passage of the brush. Lining is a movement of the whole arm, from shoulder to wrist. The brush is held lightly between thumb and forefinger on the right hand. The bristles rest on the top of the straight edge which must be held at a slight angle from the scenery, so that the brush doesn’t not blot the color from the edge of the stick. The brush is held at right angles to the work, and the trick is to keep that angle at the finish of the “run” or the stroke. Draw the brush smoothly from left to right, and if your lining is properly thinned, a smooth even line will result. It is hard to keep from pressing the brush, thus making the line uneven, but with a little practice, and even line will be drawn.”
Excerpt from “Painting Scenery, a ‘handy book’ for amateur producers” (Leslie Allan Jones, 1935, page 80)
Attached are painting details from the Pasadena Scottish Rite and Winona Scottish Rite that depict lining. Both collections were produced by Sosman & Landis Studios.