Understanding Overprint

Overprint: This function is available in all print production programs. Understanding how overprint works is essential for any designer to get the best results for his printed material.

The definition of overprint is that in most cases, when two objects of different colors overlap, they knockout - they won’t print on top of each other. To intentionally print one layer of ink on top of another is to overprint. This can be useful to terminate gaps between touching colors, for instance if a black object is printed on top of a magenta object.

This is in most cases the default setting for text set to print in default [black] color of your program, but sometimes you have to set objects and text to overprint.
In InDesign and Illustrator you can set your fills or strokes to overprint in the ‘Attributes’ palette.

Overprint preview: In InDesign and Illustrator, the results of overprinting objects can be previewed by selecting View>Overprint preview, or pressing ALT+SHIFT+CTRL+Y.
In Acrobat this can be viewed by selecting Advanced>Overprint preview, or pressing ALT+SHIFT+CTRL+Y.
A good rule is to check Overprint preview for every project, even though you don’t use overprint intentionally, to see if everything looks the way you intended.
Also, if you view your seperations you can see that overprinting objects do not knock out other objects.

Note: Overprint should be used with caution, incorrect use can produce unwanted results.