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.
Background. It is quite essential that you employ the proper background; one that is dark and gradually blended or a slightly clouded ground is recommended. This style of ground can be used for all classes of subjects.
300. The most important consideration in regard to the background is placing it in the proper light. It is exactly as essential that the background be illuminated as that the subject be, for the ground should carry out the idea of the lighting on the sitter. For this reason, when arranging the diffusing screen see that the background is properly iliuminated, and place it as far away from the subject as possible to supply good atmospheric effect. For Rembrandt Lighting see that the light portion of the background is back of the shadow side of the subject, thus supplying relief to the shadows as well as to the high-lights.
Exposure. In making these lightings expose to secure detail in the shadows, and give full time. Usually double the exposure is required for Rembrandt Lightings that is given for Plain Portrait Lightings.