Why is black referred to as “K” in printing?

Answered by Suzanne Morgan, founder, Print Buyers Online.com

Why is black referred to as “K” in printing?


The reason cited most often in our industry for referring to black as "K" is to eliminate the possibility of confusion with other printing colors, including “blue” which is one of the RGB (red, green, blue) colors. Because there is no color that begins with the letter "K" it was assigned to black.

I investigated this question further with Tom Loudon, VP Print Production at EU Services and here is what he had to say: “the letter ‘K’ in CMYK stands for ‘key’. Key is an alternate term for black ink used in multicolor printing. When letterpress was the dominant printing process, black was always the first ink down and the registration of all other colors would be ‘keyed’ to the black. Black is also key to enhancing tonal range in all four-color subjects.”
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