What is rich black?
Rich black is when under color (cyan, magenta and yellow) are added to black to make a color that is darker then the black ink by itself.
Why use a rich black?
There are different reasons for wanting a rich black. One is to create a color bridge between different colored elements. This could be a way of trapping colors. Another is to get a very dark color for the black.
What are the risks in using a rich black?
Too much ink will cause the print to get muddy and can cause offsetting where the ink doesn't dry completely and sticks to the sheet above it. We use an ink limit of 300 total ink for our offset print work. For a rich black, you really don't want to get that close to the ink limit.
What values should I use for the rich black?
If you are trying to create a color bridge we suggest using 40C-30M-30Y-100K. At it's darkest, this will give you at least a 30% bridge and will not run the risk of offsetting.
If you are just looking for a deeper black we suggest 40C-0M-0Y-100K. This will give a deep black color without running a risk of offsetting.