GB1273769A - Improvements relating to multi-colour printing - Google Patents

Abstract

1,273,769. Colour separation negatives. R. LUCAS & SON (NELSON MAIL) Ltd. July 23, 1969 [July 24, 1968], No.37136/69. Heading G2M. Colour separation negatives are produced by placing a transparent sheet over the copy of the work to be reproduced, attaching to the sheet one or more transparent screen elements each shaped and located so as to cover a corresponding area of the copy to be printed with one particular colour and each being performed with a pattern of spaced opaque or contrasting areas corresponding to the intensity of the colour to be printed in the respective area and masking or covering the entire area of each or any part of the transparent sheet which overlies an area of the copy which is to be printed with the full intensity of the colour. The colour of each part of the original is matched to one colour occurring on a colour chart, Fig. 2 to determine the required colours and densities of the three primary colours Y, R, B and of black X, e.g. the flesh tones of Fig. 3 matches with colour 5A which colour requires screen densities of value 1 in the yellow and red colour separation. The screen elements are of plastics pre-printed with a pattern of closely spaced dots or lines, the size of which are varied in accordance with the percentage of the total area of each element to be covered to produce the screens of density 1-4. One face of the element is coated with a transparent self-adhesive. The elements are provided with pre-angled base lines for ensuring proper placement of the element in accordance with a particular colour to be printed. The original is mounted upon a light table, registration pins being attached by transparent adhesive tape to the original, registration tabs being taped to each transparent plastics sheet.