Understanding Plain vs. Rich Black
There are two basic categories of black: plain black and rich black. Plain black is created using 100% black ink. Rich black, on the other hand, is created using some combination of process colors.
Although rich black is called “black,” it doesn’t look entirely black. It looks more like a very dark gray. Therefore, some black ink is generally added to the CMY mix. For example: drag out a square marquee in Photoshop, fill it with black, and you’ll see that “black” is actually C=75, M=68, Y=67, K=90.
These differences are important because using rich black rather than plain black can have different results aesthetically and during printing process.
For example, because rich black uses more ink than is really required, if you have heavy black ink coverage, you can run the risk of oversaturating the paper.
Using rich black and plain black interchangeably can also give your document an inconsistent look. This is especially true where typography is concerned. Because rich black is made up of multiple colors, you can run the risk of even minor registration errors ghosting and blurring your type.
You may want to use a rich black for aesthetic reasons, however, such as to create warmer feel. Rich blacks vary in the levels of the constituent colorants. More cyan and/or magenta tends to boost the “warmness.” More pure black tends to “cool” it down.
Just as we would never think of the color “red” or “blue” without some kind of qualification, we never assume that all black is created equal either. As always, it’s worth checking with us to see if we have any advice or cautions regarding the use of rich vs. plain black.