What is the difference between knockout and overprint?

Knockout removes the ink underneath a shape so only the top shape prints at that location. Overprint keeps both. The top ink prints directly on top of the bottom ink and the two mix. Knockout is the default for most print work. Overprint is only correct in specific cases: 100% black text, trapping, spot varnishes, and specialty finishes.

Why did my white ink disappear on press?

Because it was set to overprint. When white is set to overprint and sits on top of another color, the RIP interprets it as 'add white to the color underneath', which means nothing is added and the white disappears entirely. White ink must always be set to knockout (or have the overprint attribute stripped).

Should text knock out or overprint?

Colored text should knock out so it reproduces accurately on its background. Small 100% black text is commonly set to overprint on purpose. It eliminates white fringes from registration shift. Most modern RIPs and preflight tools enforce this automatically, but it's worth verifying in your PDF export settings.

What is Knockout in Printing? Knockout vs Overprint

TL;DR

Knockout is the default behavior of a PDF: when you put a shape on top of another shape, the press removes the ink underneath so only the top shape prints at that spot. It's the opposite of overprint. Knockout is correct for almost everything. Colored text, logos, solid fills, spot inks. The exceptions are small and specific: 100% black body text (overprint avoids registration fringes), trapping overlaps, and clear-varnish layers. White ink must always knock out. If it's set to overprint, it vanishes on press.

What knockout actually does

Imagine a red box with the word "SALE" in white sitting on top of it. When the file hits the RIP, knockout tells the press: "where the letters sit, don't print red. Leave the substrate unprinted so the white ink shows." Every plate is punched with a hole in the shape of the white text.

If that same file were set to overprint, the press would print red ink underneath the white ink. On most presses white is semi-transparent, so the text would end up looking pinkish-gray instead of clean white. On some presses it would disappear entirely.

When knockout is wrong

A few cases call for overprint instead of knockout:

Small 100% black text and thin rules. Overprinting eliminates the risk of a white fringe around letters when press registration shifts. Most RIPs handle this automatically for C0 M0 Y0 K100.
Trapping. A narrow overprinting edge where two colors meet absorbs press misregistration. See trapping.
Spot varnishes, clear finishes, and matte/gloss overlays. These are decorative layers that sit on top of the printed image. They have to overprint or they erase the art underneath.
Specialty inks in a specific stack. Sometimes a designer wants a spot metallic to print under a translucent color to get a shimmer effect. Intentional overprint, verified with the printer.

The white ink disappearing act

The most expensive knockout mistake in packaging: white ink set to overprint. On silver BOPP, clear film, and dark substrates, white is a required base layer, and if it's set to overprint, the press treats it as "add white to what's underneath," which on a color plate means nothing visible changes. The artwork prints directly onto the bare substrate. Hundreds of pouches later, there's no white showing.

Fix: make sure every white swatch has Overprint Fill and Overprint Stroke turned OFF in Illustrator (Window → Attributes). In Acrobat, use Output Preview → Overprint Preview to see exactly what the press will reproduce.

How to check knockout in Acrobat

Open the PDF in Acrobat Pro. Go to Print Production → Output Preview. In the Preview dialog, toggle "Simulate Overprinting" ON. What you see on screen is what the press will print. If a white label disappears when you toggle, you've found an overprint bug that was supposed to be a knockout.

Acrobat's Preflight panel also has a built-in check for "Overprint is used". Run it before handoff to get a structured report.

Not sure if your overprint is right?

Preflight flags every overprinted white object and every suspicious knockout, so you catch disappearing ink before it reaches press.

Check a file →

What is knockout in printing?

What knockout actually does

When knockout is wrong

The white ink disappearing act

How to check knockout in Acrobat

Not sure if your overprint is right?