GB734066A - Improvements in or relating to photomechanical reproduction - Google Patents

Abstract

734,066. Photo-mechanical reproduction. McCORQUODALE & CO., Ltd. May 21, 1954 [June 24, 1953], No. 17570/53. Class 98 (2). Colour separation negatives for production as of letterpress or lithographic printing plates which reduce the amount of coloured ink to be printed in areas corresponding to the black or darker shades of the original, and allow the black printing-plate only to give the required strength for such areas, are made by forming positive screen records (a) of the response of the original in one wave-band, (b) of the response of the original in another wave-band, and (c) of the black areas of the original, forming a negative record (d) by printing (b) and (c) successively in register on a single sheet of light-sensitive photographic material, and forming one of the desired negative records by printing similarly (a) and (d) in register; the records (a), (b) and (c) being made at different screen angles, as of 90 degrees for the yellow printer, 75 degrees for the magenta printer, 15 degrees for the cyan printer and 45 degrees for the black printer. Such records (a), (b)and (c) may be made by the methods of Specification 681,206, using blue, green and red filters for the colour records, any pair of which correspond to (a) and (b); and a specified exposure sequence involving the three filters for the black positive (c) from which a final black negative is made by contact printing. Record (d) is made by printing (b) and (c) from the same side of the light-sensitive material referred to, and record (e) by printing (a) and (d) from opposite sides in register. An example is directed, with reference to example 3 of Specification 681,206, to the production of a set in which the cyan, magenta and yellow negatives are corrected for colour and tone reproduction as well as for reduction of coloured ink for the black or darker areas.