Knockout

Knockout means cutting a hole in one color's separation wherever another color sits on top of it, so the bottom layer never gets ink in that spot at all — only the top color prints there, on bare shirt or on the underbase, instead of one ink layering directly over another. The alternative, printing both colors full and letting one physically stack over the other, is called wet-on-wet printing, and it behaves completely differently on press.

For a buyer, knockout is why a yellow star sitting inside a blue circle prints as a clean, bright yellow instead of a muddy green where two translucent inks mixed together. We've fixed logos where a designer built overlapping shapes in Illustrator without knocking anything out, and the file printed exactly as built — colors stacking and blending into shades nobody wanted anywhere near the final shirt.

Pros knock out any color sitting under an opaque color unless a designer specifically wants the blended, layered look some wet-on-wet or shadow effects use on purpose. It pairs with trapping in the opposite direction — knockout removes overlap where colors shouldn't mix, trapping adds a hair of overlap where they need to meet cleanly.

The common mistake is assuming every overlapping shape in a design file will separate itself correctly. Vector software doesn't know which colors should knock out and which should intentionally layer — that decision gets made by whoever separates the art, which is why a rushed or automated separation can leave stacked ink where a buyer expected clean, distinct colors.