"[T]he technique involves peeling the Polaroid during the development phase and re-positioning the 2 layers at intervals within the two min development time. this will producing the ghosting effect. After the developing process is finished, re-position the two layers so that they fit again like an original Polaroid and place between two heavy flat things. Make sure everything you use can be washed (I use a exacto knife, wash your hands!) because the emulsion will get all over the place and it is quite toxic."
Artwork and explanation by smallcaps