In
printing, a key plate is the plate which prints the detail in an image.When printing
color images by combining multiple colors of
inks, the colored inks usually do not contain much image detail. The key plate, which is usually impressed using black ink, provides the lines and/or contrast of the image.However, in two-color images where neither color was black, the key plate might have been printed in the darker of the two colors.
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The printing plate that prints the stamp's design and used in conjunction with a duty plate.