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.
Key plate is synonymous with keystone in the same context.
Patent Issued for Light Guide Plate, Light Guide Key Plate and Method for Manufacturing the Light Guide Key Plate
Jul 18, 2012; By a News Reporter-Staff News Editor at Journal of Engineering -- A patent by the inventor Zhu, Zhaokan (Shenzhen, CN), filed on...