The Viewer works with stereoscopic cardboard plates, in which 2 pictures are inserted. When you insert the plate in the Viewer, the picture reveals all its relief and its perspective. The color, if there is one, appears in the light.
Small holes of a PIN on the photo paper to simulate points of light thanks to the drop of colorful resin that dropped behind the photo. A very thin layer of paper to protect the back of the picture, without too absorb light. The whole is fragile and too often victim to punctures and lacera
tions. The first devices to two goals, as this viewer, appear around 1840. The process was popular until the second world war, as it became possible for individuals to make their own pictures.