Abstract: Holograms which contain gelatin as the binder are prepared by holographically exposing the holographic material by use of coherent light, developing the holographic image by a chemical or physical process and before processing, simultaneously or subsequently, treating the material with a solution of an onium compound which comprises at least one alkyl group having from 10 to 18 carbon atoms or in which the total number of carbon atoms in the substituent group is at least 15 or a polymeric compound which comprises at least one onium group in the repeating unit.

Abstract: Multicolor holograms using gelatin as the binder and having interference fringes lying in layers parallel to the substrate, the colors of which are visible by reflection in incident natural light, by treating the holographic material which has been holographically exposed and processed to produce a hologram therein, by applying to the selected areas of the gelatin which contains the interference fringes a solution of a compound which causes the interference fringes to separate permanently and produce a bathochromic shift in the replay wavelength.