Some testing with pigment saturation and tone range for tri-color gum printing. The aim is to print in “full color”* with only three separation negatives, using CMY (cyan-magenta-yellow) pigments, without the K (black) component normally used in commercial color separations. I am trying to create black by mixing from the three color layers. I will use cyanotype as the bottom layer, diluted with water to balance it better with the other colors.

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Exposure tests on Cyan (traditional cyanotype diluted with 4 parts of water), Magenta (Maimeri Magenta), and Yellow (Maimeri Cadmium Yellow).

Once the pigments and their strength are chosen, and a working correction curve created for each separated negative (e.g. by ChartThrob script), they can be tested by printing all CMY colors on top of each other. If the pigments were chosen succesfully and the negatives curved properly, the result should be, more or less, a gray balanced image.

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Cyan (cyanotype, top left), Cyan+Yellow (top right), and Cyan+Yellow+Magenta (left), each layer with its correction curve, respectively.

*A gum printer’s “full color” doesn’t necessarily look like properly balanced color photograph (if it did, why bother gum printing at all), rather it is his/her interpretation of subject colors, and can vary quite a lot, depending on pigments chosen. That said, also naturally balanced, very realistic “photographic” colors are possible to achieve.