Rich black is an ink mixture of solid black, 100% K, with additional CMY ink values. This results in a darker tone than black ink alone. If you print black alone as 100% K, the resulting black may not be as dark as you might like
We recommend using
C 60 M 40 Y 40 K 100
This will give you a deep, dark, rich black.
Want to learn more? We’ve written a great article on this subject.