In printing, a key plate is the plate which prints the detail in an image.^{[1][better source needed]}

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, contrast, or both, of the image. However, in printing in which black is not used (common in early two- and three-color printing), the key plate could use the darkest of the colors used. Key plate is synonymous with keystone in the same context.

• CMYK color model
• Key type stamp