UV Flatbed Spot Color & White Ink Vector Guide
Direct-to-substrate UV flatbed printing (onto acrylic, wood, brushed aluminum, glass, leather, and coroplast) requires precise multi-channel vector prepress. Unlike paper printing where the background substrate is white, dark and transparent substrates require dedicated vector spot channels for Opaque White Underbase, Spot Varnish / Gloss Textures, and Adhesion Primers.
🛠️ Interactive Prepress Calculator:
Calculate inward white ink underbase choke margins, pixel erosion, and spot gloss varnish spread. Launch the free UV Flatbed White Ink Choke & Varnish Spread Calculator →
1. RIP Spot Channel Naming Matrix
Every UV flatbed RIP software (RasterLink, VersaWorks, Onyx, Caldera, Ergosoft, SAi Flexi) identifies specialty ink channels by exact case-sensitive spot swatch names:
| Printer / RIP System | White Ink Swatch Name | Varnish / Gloss Swatch Name | Primer Swatch Name |
|---|---|---|---|
| Mimaki (RasterLink 6/7) | Spot_White |
Spot_Clear / Spot_Gloss |
Spot_Primer |
| Roland (VersaWorks 6) | RDG_WHITE |
RDG_GLOSS |
RDG_PRIMER |
| Canon Arizona / Onyx | Spot 1 (or Spot_White) |
Spot 2 (or Spot_Varnish) |
Spot 3 |
| Mutoh (VeriStudio / VerteLith) | White |
Varnish |
Primer |
| swissQprint / Caldera | White_Ink |
Effect_Varnish |
Bond_Primer |
2. Vector Choke & Offset Rules (Preventing White Halos)
When printing high-opacity UV white ink directly beneath CMYK color layers, mechanical carriage registration micro-drift or droplet scatter can cause a visible white border ("halo" or "peeking") around dark graphics.
3. Multi-Layer Print Order Stacks
UV flatbed workflow depends on substrate transparency and viewing direction:
- Front-Lit Opaque Substrate (Wood, Metal, Black Acrylic):
Substrate → Primer (if metal/glass) → Choked White Underbase (100%) → CMYK Color → Spot Gloss/Varnish Texture - Second-Surface Backlit Clear Acrylic (Reverse Print):
Clear Acrylic Face → CMYK Color (Mirror Flipped) → Full White Diffuser Flood → Black Blockout Layer - Double-Sided Window Graphics (Clear Glass/PETG):
Front CMYK → Choked White → Black Light-Blocker → Full White → Back CMYK
4. Essential Vector Prepress Checklist
- Vector Solid Fills Only: Spot white and varnish channels must be defined by 100% solid spot color vector polygons. Avoid raster gradients or semi-transparent drop shadows in spot plates.
- Overprint Attributes Enabled: In your vector prepress file, enable
Overprint Fillon the top CMYK layer so the RIP does not knock out the underlying white plate. - Export as PDF/X-4: PDF/X-4 preserves native spot color swatch layers and transparent overlay blending without flattening vector paths into pixelated raster tiles.