Xerox art (sometimes, more generically, called copy art, electrostatic art, scanography or xerography) is an art form that began in the 1960s. Prints are created by putting objects on the glass, or platen, of a photocopier and by pressing "start" to produce an image. If the object is not flat, or the cover does not totally cover the object, or the object is moved, the resulting image is distorted in some way. The curvature of the object, the amount of light that reaches the image surface, and the distance of the cover from the glass, all affect the final image. Often, with proper manipulation, rather ghostly images can be made. Basic techniques include: Direct Imaging, the copying of items placed on the platen (normal copy); Still Life Collage, a variation of direct imaging with items placed on the platen in a collage format focused on what is in the foreground/background; Overprinting, the technique of constructing layers of information, one over the previous, by printing onto the same sheet of paper more than once; Copy Overlay, a technique of working with or interfering in the color separation mechanism of a color copier; Colorizing, vary color density and hue by adjusting the exposure and color balance controls; Degeneration is a copy of a copy degrading the image as successive copies are made; Copy Motion, the creation of effects by moving an item or image on the platen during the scanning process. Each machine also creates different effects.