Abstract: A hologram which comprises a light transparent base having coated thereon a hydrophilic water-swellable layer which contains the holographic image and a dye whose peak absorption is below the peak replay wavelength of the hologram. The hologram is produced by adding the dye after exposure of the hologram.

Abstract: Method of preparing a hologram which is of the silver halide in gelatin binder type, which method comprises exposing, developing and bleaching the holographic material, where a water-soluble halide and a ferric salt of an acetic acid derivative are used in the bleach bath.

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.

Abstract: Holograms which contain gelatin as the binder are prepared by holographically exposing the 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 a gelatin reactive compound which has a molecular weight of over 200 and which reacts with the gelatin to form covalent bonds therewith to increase the molecular bulk of the gelatin.

Abstract: Holograms using gelatin as the binders are prepared by holographically exposing holographic material with coherent light, developing the holographic image by a chemical or physical process and before processing, simultaneously or subsequently, treating the material with an aqueous solution of a polymer which comprises a tertiary amine group.

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: A method of preparing a hologram which comprises subjecting holographic material to a holographic exposure, the holographic material comprising silver halide emulsion of which at least 80% by weight of the halide is bromide, developing the exposed material in a silver halide developing solution to yield developed silver, converting the developed silver to silver chloride using a bleaching agent selected from ferric ions, persulphate ions, chlorate ions, peroxides and water-soluble quinones, in the presence of chloride ions and then fixing out the silver chloride using a silver halide fixing agent which dissolves silver chloride but not silver bromide or silver iodobromide under the conditions of use.

Abstract: A method of preparing a hologram which comprises subjecting holographic material to a holographic exposure, the holographic material comprising a silver halide emulsion of which at least 80% by weight of the halide is bromide, developing the exposed material in a silver halide developing solution to yield developed silver, converting the residual silver bromide, in the main part at least, to silver iodide by use of an aqueous iodide solution, removing the developed silver but leaving the silver iodide either by use of a bleach/fix bath under controlled conditions or by rehalogenating the developed silver to silver bromide or chloride using a brominating or chlorinating silver bleach solution and simultaneously or subsequently fixing out the thus formed silver bromide or chloride using a fixing agent under such conditions that silver iodide is not dissolved from the material.