The following information is included for the benefit of Quark customers:

Source- Wikipedia

Black ink is used in printing for several reasons. The “black” generated by mixing Cyan, Magenta and Yellow primaries does not make a true black. Therefore, four-color printing uses black ink in addition to these other subtractive primaries. Common reasons for using black ink include:

  • Text is typically printed in black and includes fine detail (such as serifs), so to reproduce text or other finely detailed outlines using three inks without slight blurring would require impractically accurate registration (i.e. all three images would need to be aligned extremely precisely).

  • A combination of 100% cyan, magenta, and yellow inks soaks the paper with ink, making it slower to dry, and sometimes impractical so.

  • A combination of 100% cyan, magenta, and yellow inks often results in a muddy dark brown color that does not quite appear black. Adding black ink absorbs more light, and yields much “blacker” blacks.

  • Using black ink is less expensive than using the corresponding amounts of colored inks.

When a very dark area is desirable, a colored or gray CMY “bedding” is applied first, then a full black layer is applied on top, making a rich, deep black; this is called rich black. A black made with just CMY inks is sometimes called a composite black.

The amount of black to use to replace amounts of the other ink is variable, and the choice depends on the technology, paper and ink in use. Processes called under color removal, under color addition, and gray component replacement are used to decide on the final mix; different CMYK recipes will be used depending on the printing task.