18% Gray Card

The industry standard for setting exposure and white balance is a neutral gray color of 18% reflectance (some sources quote a 12% figure). Many types of cards can be purchased with this color. Other photography accessories are made in this color; I have seen micro fiber cleaning cloths and the interiors of camera bags. I found that it is best to use gray cards, manufactured to high quality standards; fortunately these are inexpensive. I have at least two; a 8" x10" for setting white balance and exposure, and another cut into small squares for inclusion in a photo for color correction. To use the gray card under continuous lighting to set exposure, place it in the scene to be photographed tilted so light is reflecting off the card and with the camera in aperture priority mode* fill the view finder with the card, depress the shutter release half way, and note the displayed shutter speed. Then, set the camera to the manual mode using the aperture and shutter setting noted before and take the photo. It would seem a dark gray card would give a false reading, but I have found this far more accurate than the auto meter built into the camera. The cards should be handled carefully and replaced if worn, to insure color fidelity.

* Shutter priority mode would also work, but for furniture/construction photos the aperture setting is of more concern than the shutter speed.