By placing said object on a surface (could be your floor, table, or chair) about a foot or two away from the window and propping up a white piece of poster board opposite the window, you are adding fill light to the scene. The shadows which were cast by the natural light streaming into the window are less obvious now — you are creating a light source on both sides of the subject. Conversely, if you add a black sheet of foam core to this same set up, you will subtract light and increase shadows, adding more contrast to your final frame. This can be used to add drama, and is typically used when darker backgrounds are in place.
I use the white foam core reflector in most of my food photography. I like the black reflector on occasion, but for those of us at Apartment Therapy, we usually want bright, punchy photos that view well on a myriad of screens. When in doubt, I go for a hair brighter rather than a hair darker on most imagery for web. So where are all these pictures from? While browsing Twitter last night, I noticed a bundle of photographs that perfectly illustrate these reflector boards in action, via Shauna, of Gluten Free Girl, who is creating her newest cookbook with Penny De Los Santos as the photographer. Notice their set up: great natural light from a large window, black and white reflectors to create different moods in the images, a ladder to get totally above the food and a whole lot of amazing props. We can all learn a lot by observing this set up, and applying it to multiple photo needs.
xoxo, Leela the Photo Magician (Images via Shauna James Ahern's Twitter feed)