This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Illuminating Background. The background for profile portraits should be quite dark and, therefore, turned from the light The darkest portion of the ground should come behind the side of the face which is nearest to the light; while on the other hand, the light part of the ground should come back of that part of the head which is farthest away from the light. With the darkest part of the ground to back up the highest lights, and the more neutral tint, or light parts, falling back of the shadows, or most dense parts of the portrait, relief and roundness are supplied to the head and figure. Watch the light as it falls upon the background. By turning from the light the end of the background farthest from the skylight, it becomes darker, or vice versa. Experimenting and closely watching results will soon enable you to overcome any difficulty in properly illuminating the background.
Securing Roundness. By working with the background a considerable distance from the subject, properly illuminating it by careful use of the diffusing and reflecting screen, by correct focusing and stopping down of the lens, proper gradation from the highest lights to the deepest shadows will be secured, and no trouble will be experienced in producing roundness.
Securing Half-Tones In The High-Lights. Half-tones in the high-lights will be destroyed if the lighting is too hard and the subject is placed too close to the side-light. This difficulty will be readily overcome if you handle the diffusing screen carefully. If the light controlled by the diffusing screen is too strong for the highest catch-lights, draw a portion of the white curtain on the skylight, and with the light filtered through this curtain the high-lights will be materially softened.
Too Large A Catch-Light In The Eyes. When the subject is placed too close to the light, or when the eyes are turned too far into the light, the catch-light will appear large. Especially in profile lightings, if you part the curtains on the diffusing screen too much, thereby allowing too strong a light to strike the eyes of the subject, a catch-light of excessive size will be produced. The remedies for these difficulties are obvious.
Eyes Appear Staring. If the pupils of the eyes have been directed too high, so that the whites are visible beneath the iris, the eyes are apt to appear staring. Be careful to have the subject's eyes directed at a proper height, so that the whites will not show. This will readily overcome the difficulty.