Black colors in print are not all the same. On computer monitors, all blacks will generally appear consistent. But on press, different ink combinations can create a wide range of blacks.
When black is the text color, Use flat 100% black (C-0 | M-0 | Y-0 | K-100) for the crispest results. If you have a solid black area larger than two square inches, we recommend using a “rick black” for a darker, more uniform color. The Rich Black color build we recommend is (C-60 | M-40 | Y-40 | K-100).
If you are intentionally doing so, make sure to ask your printer which variant of rich black they like to use on press, usually referred to as “warm black” or “cool black”, where there are higher levels of either magenta or cyan, respectively. Its generally not recommend that you use a completely saturated level of all four colors where (C-100 | M-100 | Y-100 | K-100), as this can over saturate the paper on press and will certainly give the press operator trouble.