lighting - What does a black reflector do?

I'm familiar with using white / silver / gold reflectors to add fill light to a photo. When would you use a black "reflector"?

Answer

To remove light.

If you're shooting outside, or in a place where there's lots of background light being bounced around, it might not be enough to place an item to create a shadow onto your object, since light reflected off of that item might still give you tints or light you don't want.

A black "reflector" creates shadow and doesn't reflect light (or as much light, depending on the quality) onto your object, which might help you darken it.

For instance, if you're trying to take a portrait outside, and the face gets a bit too much light on one side, a black reflector might help you reduce that by both creating a "shadow" by blocking light, and not reflecting any light onto that side of the face.