Method of making color separation plates used as a proof and a positive for making offset printing plates photographically

A method of making color separation plates used as a proof and a positive from which offset printing plates are directly made photographically comprising, creating an original art image as full color line art on a monochrome overlay by superimposing in an overlay arrangement a plurality of individual transparent supports each having a continuous color layer of coloring material on a major side surface and the coloring material of the coloring material of the individual layers of the monochrome supports each being a different color corresponding to the color of a printing ink, mechanically removing coloring material on each support sequentially while maintaining the monochrome supports superimposed to define thereon an elementary design for progressively jointly defining with the individual monochrome supports superimposed with elementary designs thereon in a registry effective to define a final original art image in a desired color for each portion of said original art image,

• while removing said coloring material continuously comparing the elementary design of the individual monochrome supports superimposed with elementary designs thereon in a registry effective to define a final original art image in a desired color for each portion of said original art image,
• while removing said coloring material continuously comparing the elementary design of the individual monochrome supports superimposed so that the complete original art image defined by the superimposed monochrome supports is revised as the elementary design on given support is changed, and
• maintaining the monochrome supports superimposed to obtain a multicolor final original art image by transparency.