In most cases, when two objects of different colors overlap they knockout — they won't print on top of each other. To intentionally print one layer of ink on top of another is to overprint.
Overprinting is sometimes used to avoid the need for trapping and avoid gaps between touching colors. Spot color intended to designate the application of spot varnish are also set up to overprint.
When overprinting black, it may be necessary to use rich black rather than a pure 100% black ink. A rich black is any black with some amount of cyan, magenta, or yellow added. One typical balanced rich black is C40 M30 Y30 K100. It will overprint other colors more effectively than a plain black.
Also Known As: surprint