White ink / underbase
Opaque white ink laid under color so artwork stays bright on dark, colored, metallic, or transparent material.
See it
What it is
Ordinary CMYK printing assumes the paper supplies white. White ink is a real opaque ink used when the stock is dark, metallic, colored, or transparent. Printed beneath color as an underbase, it gives the CMYK something pale to sit on, so a red logo stays red instead of turning dull and translucent against the material.
Reach for it on clear labels, window graphics, dark apparel, and colored packaging. The white can support the whole image, sit only below chosen objects, or print by itself as visible artwork. One hit is not always fully opaque, so demanding work may use a denser mode or more than one pass.
Gotcha: a white plate aligned exactly to the color can peek out as a hairline when registration moves. Choke the underbase slightly inside the color edge and inspect the actual separation, not just the composite preview. On clear material, also state which side is viewed and whether the print is surface or reverse, because that changes the ink order.
Ask AI for it
Build a white-underbase separation for this clear label in Adobe Illustrator. Create a spot color named White_Ink at 100%, place it on its own layer beneath the CMYK artwork, and choke its outer edge inward by 0.2mm so white cannot halo around the color. Leave intended clear windows empty. Export as PDF/X-4, then use Adobe Acrobat Output Preview to confirm White_Ink remains a separate plate and that every CMYK area requiring opacity has white below it.