Screen Printing Design: Working With the Medium

Screen printing is one of the most tactile and visually compelling print processes available. It's also one of the most technically demanding to design for. Ink sits on top of the substrate rather than absorbing into it. Colors are printed as flat, opaque layers. Registration between layers is mechanical and imperfect. Every one of these characteristics shapes how a design should be built.

I've had printer calls about files that weren't set up for screen printing. I've also had jobs come back looking worse than expected because I made assumptions about what the printer would handle automatically. Here's what I've learned.

Spot Colors Only

Screen printing works with spot colors, not process color. Each color in your design is a separate screen, a separate ink, a separate press pass. A design with six colors requires six screens, which means six opportunities for registration to drift and six separate costs.

I design screen print projects in as few colors as possible. Two or three colors is the sweet spot for most work. Five or six is where jobs start getting expensive and registration problems start getting noticeable.

This means thinking about the design differently from the start. Instead of picking colors freely and reducing them later, I think from the beginning about what the design looks like as a two-color piece, a three-color piece. The constraint shapes the composition.

Halftones and Simulated Process

When you need the appearance of more colors than you have inks, halftones are the tool. A halftone screen breaks a tonal value into a pattern of dots. Where the dots are large and close together, the ink reads as solid. Where they're small and spread out, the ink looks lighter. Two overlapping halftone screens in different ink colors can create the illusion of a third blended color.

Halftone design requires understanding the mesh count of the screens being used. Fine mesh screens hold fine halftone dots; coarser meshes need larger dots to print cleanly. I always ask the printer what mesh count they recommend for halftone work on the substrate I'm using before I set my halftone frequency.

The Underbase

When printing on dark fabrics or papers, light colors won't show without an underbase. A white or light gray ink is printed first and flashed (partially cured) to create a base that the final colors sit on top of.

This adds a color to your count. A two-color design on a black substrate with an underbase is actually a three-screen job. Factor this in from the beginning.

The underbase also affects the feel of the final print. A heavy underbase creates a raised, plastic feel. A thinner underbase or a soft-hand underbase feels more integrated with the substrate. I specify underbase weight and type explicitly rather than leaving it to the printer's default.

Trapping Between Colors

Where two colors sit adjacent to each other, registration drift can leave a gap between them or a double-printed overlap. Trapping is the technique of slightly expanding one of the colors so it overlaps the adjacent color by a small amount, ensuring no gap appears even if registration isn't perfect.

Standard trap is 0.5pt to 1pt on each side. On very textured or flexible substrates, I'll increase this to 1.5pt or 2pt. I build trap into my files before sending to the printer rather than asking them to do it, because I know my design intent better than they do.

Testing Before Production

For any significant screen print run, I request a strike-off (a test print) before approving the full production run. Colors shift between screen and print. The interaction between specific ink colors and specific substrates is unpredictable until you see it. A strike-off is cheap insurance against a full run of incorrect color.

Screen printing rewards designers who understand and embrace its logic. The limitation is the aesthetic.