Black and white photographs can portray a higher level of timelessness than color images. The lack of color also gives us a better sense of the time and mood behind a portrait. Because of these characteristics, black and white photography has maintained a strong presence in portraiture. Since the eye perceives black and white photography differently than color photography, the process behind creating compelling black and white portraits is also a little different. Here are a few pointers to get you started:
1. Black and white photography is all about lights and shadows
These two things, when combined, create contrast. Contrast is essential to black and white photography and part of what makes it so appealing. The real task here is finding a good balance between the two. It's true that bright whites and black blacks are key to monochrome portraiture, but don't forget the grays. An assortment of grays in a black and white portrait will offer some much needed separation between the highlights and shadows.
2. Shoot in RAW
By doing so, all of the images pixel data will be preserved and will give you greater control of your image in post. If your camera has a RAW + JPEG option, use that. You can then set the JPEG to shoot in monochrome which will give you a black and white image in your viewfinder, all while having the added benefits of shooting in RAW.
3. Know what colors look like in black and white
For example, the color red will look black in a black and white photograph. If the model is wearing a red dress and you are shooting against a dark colored background, the two may blend together resulting in a dull, flat portrait.
4. Shoot on a low ISO
This will help avoid any grain in your photograph, which could be made more noticeable in a black and white photo, namely in the shadows. If at all possible, try to keep your ISO around 160. Many modern DSLR's default at 160 and that's not without reason. It is fast enough for most portraiture and produces sharp, clean photographs.
5. Utilize texture and shapes
Similar to color portraits, using shapes, lines, and silhouettes can aid in a photographs composition. These, along with textures and patterns, are made more noticeable in black and white portraits because the eye is naturally drawn to the contrast of the image instead of the detail. For example, the weathering on an tree is initially more noticeable than tree itself, because our eye first goes to the contrast created between the age spots on the wood.