Black is not one thing in process printing. A single black plate produces a dependable 100K black; combinations of CMYK inks can create a visually deeper rich black.
Use 100K for small detail
Fine text, rules, barcodes, and registration-critical marks should normally use black ink alone. If four plates form tiny letters, even a small registration error can create colored fringes and softness.
Use rich black for large areas
A broad black background may look gray or thin with black ink alone. A controlled support of cyan, magenta, and yellow can add density. The correct formula depends on the press and paper, so ask the printer instead of relying on a universal recipe.
Watch total ink coverage
Adding four percentages produces total area coverage. Excess ink can cause drying, setoff, detail loss, or paper problems. Output profiles manage this limit for a specific production condition.
Check overprint settings
Black text is often configured to overprint to reduce registration risk. Large objects and reversed elements need deliberate treatment. Use your PDF preflight and separations preview before release.