Why Does a Dark Printed Carton Show White Cracks Along Its Folds?

Find out whether the defect exists before folding

Preserve a flat printed sheet and a folded sample from the same production condition. Compare the dark artwork along the intended crease before and after folding.

If the white line is already present on the flat sheet, inspect printing, artwork separation and registration. If the flat print is continuous but white fractures appear after folding, investigate the physical surface and crease.

Holmen's paperboard guidance explains that paperboard should be creased before folding. The crease creates a controlled hinge and reduces the risk of disfiguring cracks in printed, varnished or laminated surfaces.

Do not automatically describe every pale fold line as missing ink. A physical crack may expose underlying board layers or interrupt a coating. Conversely, a clean physical fold can still have a misplaced printed border caused by artwork alignment.

Record which side of the fold shows the defect, whether it follows the entire crease and whether the problem is repeatable across samples.

Inspect the board and crease construction

Ask the supplier for the exact board grade, thickness, grain orientation, surface treatment, crease configuration and folding direction used in the sample.

Holmen's technical guidance explains that creasing behavior depends on board properties, moisture, grain direction, coating and tool geometry. It also documents that inadequate creasing can cause surface cracking or an undefined fold.

A dark, heavily covered panel may make a pale fracture especially visible, but dark artwork alone does not establish why the surface cracked. Compare the actual physical condition rather than assuming that changing the black ink value will solve it.

Inspect whether the carton was folded in the intended direction relative to the crease bead. Also determine whether the supplier changed board stock or crease tooling between samples.

Do not prescribe a universal groove width or pressure adjustment. Those settings belong to the converter and depend on the selected board and equipment.

Hypothetical dark carton comparison

Hypothetical exercise—not a manufacturing test: fictional carton D4 uses a dark navy printed panel crossing a vertical fold.

Sample A is a flat printed sheet with continuous navy artwork. Sample B is stipulated to use the same artwork and board but to show a pale fractured line after folding. That comparison would support a fold-related physical mechanism.

Sample C is a proposed supplier-adjusted crease construction. The merchant should request a new folded proof and inspect whether the navy surface remains intact without causing another structural defect.

If a second production sample uses different board stock, it cannot isolate the crease change alone. Record every material or process difference.

The worksheet contains proposed observations and actions; no carton was folded or inspected for this manuscript.

Approve the erected carton, not only the flat artwork

Compare the actual folded carton with the approved physical sample. Inspect cracks, panel shape, crease placement, legibility and the integrity of the printed surface.

If the defect is mechanical, ask the converter to evaluate the appropriate board and crease treatment. If the artwork itself crosses a fold in a way that makes a critical element vulnerable, consider a separately approved layout adaptation.

Do not conceal physical cracking by digitally painting the fold dark in a marketing mockup. A corrected preview would not repair the manufactured surface.

Keep the exact board specification, printed-file revision, crease configuration and accepted folded sample together. A change in substrate or finishing process can invalidate the earlier approval.

Record your own observations

The filled rows are illustrative examples. Use the blank row for your own files and observations.

Download the editable CSV worksheet

What the references establish

• Holmen/Iggesund — Die-cutting and creasing: Primary paperboard-manufacturer guidance on cracking, crease geometry, material properties and production variables.
• Holmen — Creasing and folding: Explains why paperboard is creased before folding and how a controlled hinge protects the surface.
• Holmen/Iggesund — Creasability and foldability: Documents coating integrity, directional material properties and fold-related mechanical behavior.