Stereoscopic Autochromes were especially popular, the combined color and depth proving to be a bewitching experience to early 20th Century eyes. Usually of a small size, they were most commonly viewed in a small hand-held box-type stereoscope. Larger, non-stereoscopic plates were most commonly displayed in a diascope, which was a folding case with the Autochrome image and a ground glass diffuser fitted into an opening on one side, and a mirror framed into the other side. The user would place the diascope near a window or other light source so that light passed through the diffuser and the Autochrome, and the resulting back-lit, dark-surrounded image would be viewed in the mirror. Slide projectors, then known as magic lanterns and stereopticons, were a less common but especially effective display technique, more suitable for public exhibitions. Unfortunately, projection required an extremely bright and therefore hot light source (a carbon arc or a 500 watt bulb were typical) and could visibly "fry" the plate if continued for more than two or three minutes, causing serious damage to the color. More than a few surviving Autochromes suffer from such "tanning" and conventional projection is not a recommended means of displaying these irreplaceable images today.