100% black (K only) can look gray on coated stock or in large areas. Rich black (K plus CMY) looks denser but can cause registration or trapping issues if not set up correctly.
When to use 100% K
Small type and fine lines should stay K only. Rich black can cause slight misregistration and soft edges. For body text and thin rules, 100% K is correct.
When to use rich black
Large solid black areas benefit from a rich black build (e.g. 60C 40M 40Y 100K) so they do not look washed out. Use a single, consistent build; mixing builds in one file can cause visible differences.
Rules of thumb
• Type and fine detail: 100% K only.
• Large areas: rich black with a defined build; ask your printer for their standard.
• Do not mix multiple rich black recipes in the same job.
Common mistake
Using rich black for small type. Registration drift can make type look fuzzy or colored. Reserve rich black for large solids only.