Underbase, choke and trap

On dark garments, an underbase (usually white) is printed and flashed under the top colors. Choke the underbase, making it slightly thinner than the colors on top, so white doesn’t peek out if registration shifts. A commonly cited starting point is roughly a quarter to three-quarters of a point; the right number depends on how well your press holds registration, so test it.

Spread (or trap) is the opposite move: enlarge a color slightly so it overlaps its neighbor and hides small registration shifts.