In Japanese woodblock printing, the key block carries the main outlines of an image.
The keyblock, often called the black block, established the composition’s principal contours and important details. In a multicolor print, separate blocks were then carved for different colors. The printer aligned each sheet against registration marks so that the colors fitted the outlines and one another accurately.
This division of labor explains why an ukiyo-e print was a collaborative object rather than the work of the designer alone. The artist prepared the design, the block cutter transferred and carved the image, and the printer applied inks and paper under the publisher’s direction. The keyblock is sometimes confused with a color block, but their functions differ: the keyblock defines outlines and structure, while color blocks supply areas or gradations of pigment. Japanese registration marks are called kentō.