For those who don’t know, overprinting is the process of layering colors in the printing process. In traditional 4 color process, overprinting (and especially the sequence of colors) is important to keep segments of color looking seamless next to each other. A combination of trapping and making sure darker colors print last (or over — get it, overprinting?) help with this effect.
Overprinting can also be used as an effect in printing by multiplying overlapping colors to produce additional colors. Here’s 5 examples of creative overprinting with some interesting results.