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.
302. As only a small source of light is required in making front or two-thirds views of Rembrandt Lightings, it is fully as easy to produce these effects in the home as under a studio skylight. It must be remembered, however, that a small source of light always tends to produce contrast and harshness. For this reason great care must be exercised in diffusing the light sufficiently to secure a gradual blending between the highest points of light and the deepest shadows. If the light is not properly handled to produce softness, or if insufficient exposure to obtain full detail in the shadows is given, the high-lights will be so hard and so extremely chalky that, no matter how the developer is manipulated you will not produce a soft negative.
303. It is only by proper diffusion of the high-lights with sufficient illumination in the shadows, accompanied by correct exposure and accurate development, that the very best results are obtained. No matter whether Rembrandt or Plain Lightings are being made, if an extremely contrasty source of light is employed, and the shadows are not sufficiently illuminated, you will in almost every case suffer lack of detail in the shadows, no matter how far the negative is carried in the development. If carried beyond a certain stage, even with sufficient exposure the high-lights will become chalky, the shadows, instead of building up in detail, will merely fog over, and the resulting print will be only a mass of black and white, with absolutely no intermediate half-tones.
304. Care must be taken that the face is not turned into the light more than sufficient to produce the proper effect of lighting, as the result will be large, strong catch-lights. Besides, by so doing, the light is allowed to spread to too great an extent over the face. Strong light also causes the pupils to contract and become small, and the expression is by no means as good as when the pupils are larger or more dilated
Normal Rembrandt Lighting. To produce a full, or nearly full, face portrait in Rembrandt Lighting, place the sitter in exactly the same position as you would for Plain Portrait Lighting, locating the camera further from the light and viewing the subject from the shadow side. It may be necessary to place the subject a trifle closer to the light, this depending entirely upon the height of the window, as the light must fall upon the subject in exactly the same manner and at the same angle as for a Plain Lighting, which is about 45°.
Diffusing Screen. The diffusing screen on the window is a very important accessory in correctly making Rembrandt Lightings. By employing it judiciously you regulate the strength of the high-lights, and require less use of the reflecting screen to illuminate the shadows. When direct rays of light enter a room, unobstructed, and fall upon the subject, they will produce extreme contrast, resulting in strong high-lights and dense shadows, with absolutely no half-tones. By gradually diffusing the source of light with the diffusing screen on the window, the white, chalky high-lights on the face will be softened. Diffusion of the source of light causes a more uniform distribution of the rays of light throughout the room. This actually shortens the required amount of exposure.
307. Equipped with a diffusing screen and a reflecting screen you have absolute control of the light. The diffusing screen can be adjusted to various heights, and if light admitted below the screen is too strong, it may be advisable to hang a piece of cloth (denser than the screen) underneath it. This will cut off, to a great extent, the rays of light which would otherwise come in at the bottom of the window. Drawing the curtains of the screen together at the bottom, allowing them to be partly separated at the top, will, as stated in the "Brief General Instruction," also assist in softening and diffusing the light on the drapery - the V-shaped opening permitting the strongest light to fall on the face.