For the process of creating these photos, I used both a white and black poster boards; and using different ISO exposure on my camera to create the different exposures. The white and black surfaces look similar in automatic settings because of the camera using one ISO sensitivity. The camera automatically assumes what setting to use to take the photo. For the black poster board I used ISO 640 to get the board to look black and for the white board I used ISO 1600 to get it to look white.
Generally it is best to change exposure by changing exposure compensation. Although you did change exposure, your method can introduce noise into photo as you raise ISO.