Every commercial screen printer has witnessed the nightmare: 500 black ring-spun cotton t-shirts printed on an automatic carousel, only to discover a bright white fringe peeking out along the edge of your top colors under the shop lights. The customer notices the white halo immediately, and the entire job gets flagged for reprint.
The cause is almost always improper underbase choking during the prepress phase. In this guide, we break down the physics of plastisol ink shear, textile stretch, and the exact vector choke tolerances needed for M&R, Roq, and Vastex carousels.
1. What Is an Underbase Choke and Why Is It Necessary?
When printing light or vibrant colors (such as Athletic Gold, Royal Blue, or Orange) on dark garments, textile fibers absorb light, turning top inks dull and dingy. A solid white underbase layer acts as an opaque primer coat.
However, commercial screen printing is a mechanical process involving fabric stretch, squeegee pressure, platen adhesive tack, and carousel indexing tolerances. If your white underbase is printed at 100% of the graphic size (1:1 with top colors), microscopic micro-shifts in registration will cause white ink to stick out past the borders of the top color.
Choking means shrinking the outer perimeter of the white underbase inward by a fraction of a point, allowing the top color to trap over the edge of the underbase and seal it completely.
2. Choke Tolerance Table by Garment Type and Mesh Count
Different fabrics and screen meshes require different choke values. A 100% heavy cotton t-shirt holds registration more firmly than a 3.8 oz tri-blend or stretchy 95/5 polyester athletic jersey:
| Fabric Type | Underbase Mesh | Top Color Mesh | Recommended Choke |
|---|---|---|---|
| 100% Carded / Ring-Spun Cotton | 110 – 156 Mesh | 156 – 230 Mesh | 0.50 pt (0.17 mm) |
| 50/50 Cotton/Poly Blends & Hoodies | 110 – 137 Mesh | 156 – 200 Mesh | 0.75 pt (0.26 mm) – INDUSTRY STANDARD |
| Tri-Blends, Rayon & Ribbed Knit | 137 – 156 Mesh | 200 – 230 Mesh | 1.00 pt (0.35 mm) |
| 100% Performance Poly (High Stretch) | 156 – 180 Mesh (Low-bleed) | 230 – 280 Mesh | 1.25 pt (0.44 mm) |
3. Step-by-Step Adobe Illustrator Formula for Perfect 0.75pt Chokes
For vector artwork in Illustrator, creating a clean choked underbase takes less than 60 seconds when executed properly:
- Duplicate All Art to Underbase Layer: Select all vector artwork that requires ink coverage. Copy and paste into a dedicated layer named
WHITE_UNDERBASE. - Merge via Pathfinder: Open Pathfinder (
Window > Pathfinder) and click Unite to merge all overlapping vector shapes into a solid composite silhouette. - Offset Path (Choke): With the merged shape selected, navigate to
Object > Path > Offset Path. Enter-0.75 pt(ensure the minus sign is included!) with Joins set to Round or Miter (limit 4). Click OK. - Delete Outer Boundary: Ungroup the object (
Cmd/Ctrl + Shift + G) and delete the original outer path, leaving only the newly generated 0.75pt choked inner path. - Assign Spot Swatch: Fill the layer with a spot color named
Base Whiteset to 100% tint.
4. Eliminate Prepress Bottlenecks Overnight
When your shop is juggling 15 jobs a day, manual underbase calculation and spot color separations consume hours of valuable art room labor.
At Orbit Design Lab, every file we prepress for screen printing automatically includes:
- Accurate 0.75pt underbase choke customized for your garment type.
- Registration marks, centerlines, and job information headers on all film layers.
- Separated Spot PMS swatches ready for direct rip output.
- Delivered by 8:00 AM EST every morning.
Need Spot Separations & Choked Underbases Done Tonight?
Send us your multi-color artwork before 5:00 PM EST. We will separate your PMS spot colors, choke your white underbase, and deliver production-ready films by 8:00 AM tomorrow.