Rich black
Black built from all four inks instead of black ink alone, used to make large dark areas look deep instead of grayish.
Plain black ink (100% K) printed over a large area can look a little flat or charcoal. Adding some cyan, magenta and yellow underneath gives a deeper, denser black.
When to use which
- Small text and thin lines: 100% black only. Four inks have to land in exactly the same spot, and on fine type any tiny shift shows as a colored fringe.
- Big backgrounds and large black shapes: rich black. A common mix for paper is C30 M20 Y20 K100.
Avoid setting everything to 100% of all four inks. Too much ink on paper can smear, crack at a fold or take longer to dry.
One more thing we watch for: a file with two or three slightly different blacks in it. They look the same on screen and print as visibly different blacks side by side.
