Patent GB-202042-A (GB)
Title: Improvements in methods of photographic reproduction in colour
IPC: G03C7/00
Filed: 1922-05-12
Abstract: 202,042. Trist, A. R., and Bawtree, A. E. May 12,1922, Colour photography; photo-mechanical printing- surfaces. - In photographic colour reproduction with a standardized process, the colours of the original or of a screen-plate. transparency or projection thereof, in the case of an original such as a landscape, are falsified to a predetermined extent so that the reproduction is an accurate copy of the colours of the original. After adopting standards for the platen, filters, &c., a chart a, Fig. 1, is prepared of which the part b carries bands of say 12 different colours approximately representing all possible colours, the part b<1> carrying the same colours printed in dots covering only half the surface, leaving the other half white. Transversely across the bands b, b<1> are printed bands c, c<1>, Fig. 2, of black dots, the black areas being 25 per cent and 75 per cent respectively of the total, these bands projecting beyond the twelve coloured bands as shown. Thus the colour white is produced in three shades, and each of the other colours in six shades. This chart is held in a frame d, Fig. 3, across which tapes e are stretched so as to partition the colour squares from each other. The frame d is held in an outer frame f, Fig. 4, carrying a glass front g. The chart a is then photographed in colours., omitting all local treatment. Next squares of thin celluloid coloured in various tints of e.g. lissamine red, lissamine green, and. acid yellow, are placed over the colour squares in the chart, which is then again photographed, and this process is repeated until the reproduction is coloured exactly like the uncorrected chart. Hence, if the operator has two charts a, one corrected and the other uncorrected, he can at once tell what change to make in any colour subject to cause it to reproduce correctly. The chart could be made circular and an auxiliary chart showing the various correcting colours, both alone and crossed with reference letters corresponding to the corrected chart, can be used, so that an operator can mix on his palette the colour necessary to change any given colour to the modified form. For the painting, transparent lake colours are prepared from the dyes used in preparing the modifying-films and ground to form oil or varnish colours. They are applied to the original direct, e.g. to pottery, or, if it is a flat subject, to a sheet of transparent celluloid stretched upon a frame which is affixed over the original. For original such as landscapes, which cannot be modified, a screen plate colour transparency of the chart is taken, and a pool of celluloid varnish poured on it and squeezed to form a thin sheet. The transparency is then corrected until its reproduction is sufficiently like the original chart, and the resulting corrections are then embodied in convenient guide charts. Then, to reproduce a subject, a screen plate colour transparency is made, protected by celluloid varnish &c., corrected according to the chart, and printing-surfaces produced from the corrected transparency. The correcting may be done on an enlarged image of the screen plate transparency, the reproduction being performed upon the projected image.