Automatic trapping in InDesign—either as built‑in trapping or Adobe In‑RIP Trapping—nearly eliminates the need for manual overprinting. However, manual overprinting can be an effective solution in the rare cases when you can’t use automatic trapping.

Use the following guidelines to determine whether or not to use overprinting:

• Consult with your service provider to see if their output devices support manual overprinting.

• Overprint when the artwork doesn’t share common ink colors and you want to create a trap or overlaid ink effects. When overprinting process color mixes or custom colors that don’t share common ink colors, the overprint color is added to the background color. For example, if you print a fill of 100% magenta over a fill of 100% cyan, the overlapping fills appear violet, not magenta.

• Don’t overprint when using a stroke to trap two process colors. Instead, you specify a CMYK stroke color that uses the higher value from the corresponding inks in each original color.

• Make sure that you and your prepress service provider agree on when and how to overprint manually, because doing so will significantly affect trapping options specified in the Print dialog box. Overprinting is supported by most, but not all, PostScript Level 2 and PostScript 3 devices.