White Ink and Underprint on Clear and Metallic Packaging

What a white underprint does

Process colors can allow clear or metallic substrates to influence the viewed result. White ink behind the graphics can reduce that influence, but the result depends on the ink, substrate and printing construction. White is not necessarily printed first: surface printing and reverse printing can require different ink sequences. Confirm color and hiding expectations with the converter rather than assuming a paper-like result.

White placement is also a design decision. A flood covers the agreed area, while selective white leaves other areas without white backing. Positive white type uses white ink; reverse white type can be formed by knocking lettering out of color over a white backing. A clear window requires omission of white and any other inks or treatments that would obscure it. Plan these distinctions before proofing.

• Full white flood: white across the agreed area; confirm hiding and color appearance by proof
• Spot white: white only behind graphics, clear or metal shows elsewhere
• White knockout: white removed where you want the substrate visible through art
• Positive white: white type or shapes printed without overlying color; distinguish this from reverse type knocked out of color

How white ink is built in the file

A named spot separation is one way to supply white artwork. Ask the converter for the exact name, object or layer structure, and overprint or knockout settings before building it. Overprint controls interaction between PDF objects; it does not establish physical ink order. Where white is supplied as a spot ink in the PDF, prepress tools can inspect it as a separate ink channel. Digital and plated workflows may require different preparation.

White and color registration can affect visible edges and fine detail. Ask the converter about minimum features, screened effects and whether white should be choked, spread or matched to the color geometry. Agree who applies those adjustments and at what stage; do not assume trapping will automatically be added during rendering.

• Name the white spot color exactly as your printer specifies
• Use the converter's specified overprint or knockout settings and verify the resulting separations
• Use editable vector geometry where practical, and agree who applies choke or spread
• Confirm supported gradients, screened effects and minimum detail before using them in white artwork

Opacity, ink film and coverage decisions

White hiding depends on the ink, substrate and printing process. Describe the desired appearance and ask the converter which construction can achieve an acceptable result, including whether multiple white applications are appropriate. An artwork tint percentage is not a measured opacity value. If screened white is intended, agree its construction and evaluate a representative proof.

On metallic substrates, color over white may still look different from the same color printed on paper. Ask to see a proof on the actual substrate. If exact brand color matters, request a drawdown or press proof rather than relying on a monitor simulation alone.

• Specify opacity as a result, not a press setting
• Ask whether a second white hit is recommended where full hiding is required
• Screened white tints are a design tool, not a substitute for opaque white
• Proof on the real substrate for metallic jobs

Checking the white plate with separations preview

Before sending files, inspect the PDF separations in a print production tool. Acrobat's Output Preview can toggle ink channels, display ink coverage and show a single selected plate as black for easier inspection. Color warnings can flag unintended rich black on type. Paper-color simulation uses the selected simulation profile; it does not establish how clear film, metallic reflection or physical white-ink opacity will appear.

Note that onscreen separation preview does not show trapping, halftone screens, resolution or printer marks; those are confirmed with your print provider using proofs. Treat the preview as a geometry and ink-assignment check only.

• Toggle the white separation alone to confirm its shape and size
• Toggle white off to see what prints directly on clear or metal
• Check color warnings for rich black on fine type
• Check for unintended inks and confirm permitted color spaces with the converter; PDF/X-4 can contain managed RGB
• Remember hidden layers are excluded from onscreen previews

File format and handoff

Industry groups such as the Ghent PDF Workgroup recommend PDF and PDF/X for exchanging packaging and label jobs. PDF/X-4 is one option. Adobe recommends creating it from your design application, and Acrobat Pro can also convert an existing PDF using the press-ready save option. Confirm with your converter whether they want the white ink as a named spot separation, a dedicated layer, or a separate file. Follow their instructions on printer marks and dieline separation.

Keep an editable source version of the white artwork for corrections. Raster white and transparency effects may be supported, but confirm their preparation and export requirements with the converter, and inspect the exported white separation.

• Ask the converter which PDF/X flavor and white construction they prefer
• Preserve the converter's required white separation through export, including any approved raster content
• Follow the converter's guidance on marks, layers and bleed
• Send source files or a layered PDF if requested for prepress edits

A simplified worked example

Consider a purely hypothetical flat-panel exercise, not a manufacturable dieline. A clear rectangular label face measures 100 by 150 millimeters. A 60 by 60 millimeter brand-colored panel is centered on it. Reverse white lettering is knocked out of the color panel while white backing remains beneath the letters. A 20 by 150 millimeter strip along the right edge is intended to remain clear, with no white or other obscuring print.

The white plate would cover the 60 by 60 millimeter panel, about 3,600 square millimeters, before any converter adjustment. If the converter chose a hypothetical 0.2 millimeter choke on each side, the white would be about 59.6 by 59.6 millimeters, roughly 3,552 square millimeters. The panel spans 20 to 80 millimeters across the 100 millimeter width. The 20 by 150 millimeter strip spans 80 to 100 millimeters and does not overlap it. The strip, 3,000 square millimeters, is knocked out of white entirely. The face is 15,000 square millimeters. Subtracting the 3,600 square millimeter panel and the 3,000 square millimeter strip leaves 8,400 square millimeters. That area could be flooded with white or left as open substrate, depending on the design. These numbers are hypothetical; the converter's dieline and trap values govern the real job.

• Panel art 60 by 60 mm; white size adjusted only per converter choke or spread
• Window strip 20 by 150 mm kept free of white and other obscuring print
• Remaining 8,400 square mm decided as flood white or open substrate

Decision guide: white strategy by goal

Use this table to choose a white approach during design, then confirm the choice with your converter before file handoff.

Pre-proofing checklist

This checklist is Teal's editorial planning framework for a white-ink job; the cited sources cover only the underlying PDF and preview principles, not your specific project. Run it before every handoff.

• White ink named, colored and set to overprint per converter instructions
• White geometry verified in separations preview, toggled alone and off
• All knockouts and windows confirmed against the dieline
• Extend white into bleed where required for the intended design; keep agreed windows and open areas free of white
• Color warnings reviewed for rich black on small type
• Proof requested on the actual clear or metallic substrate
• Trap, screens, marks and resolution confirmed with the print provider
• Converter's preferred file format and layer structure followed

Scope and limits

This guide offers planning recommendations, not press specifications or compliance determinations. The cited sources document PDF handling and preview capabilities, not white-ink performance on a particular substrate. Digital presses can print physical white ink without a conventional plate; supported separations and ink construction depend on the equipment and converter. Agree project-specific requirements and evaluate representative proofs or press samples.

Questions about white ink underprint on clear and metallic packaging