Color theory defining the CMY primaries as substances that "absorbed" only one of the retinal primary colors: cyan absorbs only red (−R+G+B), magenta only green (+R−G+B), and yellow only blue violet (+R+G−B). It is important to add that the CMYK, or process, color printing is meant as an economical way of producing a wide range of colors for printing, but is deficient in reproducing certain colors, notably orange and slightly deficient in reproducing purples. A wider range of color can be obtained with the addition of other colors to the printing process, such as in Pantone's Hexachrome printing ink system (six colors),
Combination printing often necessary to add artistic techniques to photographs. Discussing the benefits of composition in the art of photography and using combination printing, Robinson wrote, in "Pictorial Effect in Photography", that the method of combination served to "produce an agreeable presentation of forms and tones, to tell the story which is to be elucidated, and to embody the spirit of what it is intended the picture shall represent or suggest." His writings show his knowledge and his passion for creating new content in his photos with using this process. During the Victorian Era, another proponent of the technique of combination printing