What is Gelli Printing?
The basic printing technique is simple. One spreads paint over the plate with a brayer, lays a sheet of paper over the paint, rubs the back of the paper a bit and pulls it up. The wet paint adheres to the paper. The interest and uniqueness of the prints comes in by the marks made in the paint before laying the paper down.
The materials used for printing on are almost as limitless. Any paper can be used. Fabric, plastic/acetate sheets, different types of tape, cardboard, wooden boards, sheet metal, almost anything that paint will stick to can be used. The prints are used in many different artistic applications. (taken from the Wikipedia article on "Hectograph")