GB205152A - Improvements in or relating to photographic reproduction processes by means of a phosphorescent medium - Google Patents

Abstract

205,152. Landau, A. L., and Landau, M. July 4, 1922. Reproduction by a phosphorescent medium; printing-apparatus; developing.-Relates to a method of photographic reproduction by the use of a phosphorescent screen such as described in Specification 160,739, and comprises (1) a modified process and apparatus for such processes; (2) light filters for such processes; (3) methods of making the phosphorescent screens. A highly restrained developing composition is also described. In the present process an activated phosphorescent screen is placed in contact with the original and exposed to dissipating radiation through the original. The apparatus consists of a framework having a fixed glass platen 6. A glass carrier 12 is movable vertically into and out of contact with the platen 6 by linkwork 22. Guides 40 for light filters, electric lamps 34, and reflectors 36 are arranged below the platen 6 and above the carrier 12, and a door 42 can hold a book so that a single leaf thereof may be placed on the plate 6 when the door 42 is closed. In operation a phosphorescent screen 50, with its active surface downwards, is secured to the underside of the carrier 12 by clips 48 and is excited to phosphorescence by switching on the lower lamps 34. The picture to be copied is placed on the platen 6, face uppermost, and the screen 50 and the picture are pressed into contact by depressing the handle 26. The lower lamps 34 are then again switched on, the light therefrom being given a dissipating character by passing it through a light filter placed on the lower guide 40 so as to produce a phosphorescent image on the screen 50. The lights are then switched off, the original picture is replaced by a piece of photographic paper and the screen and the paper are pressed into contact. The process described in Specification 160,739 may be carried out with this apparatus, the top lamps 34 being used to produce the dissipating radiation. The composition of a suitable developer is described. (2) The light filter opaque to actinic but transparent to dissipating radiation may consist of a gelatine film dyed yellow, a sheet of amber glass, ordinary undyed paper or other organic fabric. If the phosphorescent screen has a backing of thick paper a separate light filter may be dispensed with. In copying pictures, or matter typed in coloured inks, and the like, in which dyes are used, filters are employed to remove the infrared portion of the dissipating rays, as coloured matter appears to be transparent to infra-red rays and results in poor reproduction. A filter of nickel chloride is suitable for copying blue and violet inks, a filter of nickel red glass combined with a filter of flashed red glass or other material opaque to actinic radiation is suitable for copying green inks, and a bottle green glass filter is suitable for copying red inks. (3) To produce the phosphorescent screen a povdered phosphorescent substance is mixed with a medium such as collodion, varnish, or gelatine solution, and the mixture is poured over a sheet of paper or celluloid, and after the powder has settled the excess of medium is poured off. Alternatively the medium holding the powder is flowed over a glass surface and after drying is stripped off as a film and secured by the side which was remote from the glass to a paper, celluloid or other backing by an adhesive. The backing is preferably longer than the screen so that it mav be secured to the carrier by the clips 48. Phosphorescent sulphides such as those of zinc and calcium are preferably used for the screen. (4) a highly restrained developer for the reproductions which are preferably over exposed consists of hydroquinone (4 grains), sodium carbonate crystals (160 grains), potassium bromide (2 grains), sodium sulphite (24 grains) and water (3 ozs.).