Black is often referred to as "key" in printing because the black printing plate historically held the most detail and was used as a key for aligning the other color plates.
Here's a more detailed explanation:
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Key Plate Defined: In older printing processes, the "key plate" or "key" was the printing plate that contained the majority of the image's details.
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Black's Role: This key plate was very often used for the color black, as black ink was good at showing fine detail and providing contrast.
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Registration and Alignment: The key plate served as a guide for aligning the other color plates (cyan, magenta, and yellow in CMYK printing). Printers would align the other colors based on the black key plate to ensure accurate color registration, meaning that colors line up properly to create the intended image without blurring or misalignment.
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Why "Key"? The term "key" signifies its importance as the plate key to accurate color reproduction. It served as a reference point for all other colors.
In summary, black is referred to as "key" due to its historical role as the detail-rich plate used for aligning all other colors in the printing process. This made it the literal key to accurate image reproduction.
