White toner presses need a defined white layer or spot color that the RIP maps to the white station. The same design principles as white ink apply: underbase under color, or spot white on top. File format and spot name must match the printer's setup.
What to provide
A separate layer or spot color for white, with no flattening into CMYK. The spot name (e.g. “White,” “WHITE”) must match what the printer's RIP expects. Underbase should sit under color; overprint/knockout must be correct.
Format and delivery
PDF with layers preserved, or native file if the printer accepts it. Do not merge white into process or the RIP will not see it. Confirm with the printer whether they need PDF/X or a specific version.
Checklist
• White as spot or dedicated layer, not part of CMYK.
• Spot name matches printer's specification.
• Overprint/knockout set correctly for underbase or spot white.
Common mistake
Sending a flattened PDF or a file where white is built as “no ink” (knockout only). The press has nothing to map to the white station. Keep white as a positive layer or spot.