Underbase and Halftones in Screen Printing, Explained

Two techniques do most of the heavy lifting behind a great screen print, and most people have never heard of either. Underbase is what makes colours pop on dark fabric; halftones are what let a handful of solid inks reproduce gradients, shadows and photographic detail. Together they’re the reason a screen print — a process that lays down flat, opaque ink — can produce results that look smooth, vibrant and detailed. Understanding them won’t just impress your printer; it’ll help you design artwork that actually prints the way you imagine.

What an underbase is and what it does

An underbase is a layer of white ink printed beneath the coloured inks, used primarily on coloured and dark garments. Because ink is semi-translucent, colours printed straight onto dark fabric look dull and muddy. The white underbase creates a bright, neutral surface so the colours on top reflect light and appear true and vivid — exactly as they would on a white tee.

• The underbase is printed first, then flash-cured (partially set) so the next inks don’t bleed into it.
• It’s shaped to the artwork — usually a slightly reduced “choke” of the design so white doesn’t peek out at the edges.
• It dramatically boosts colour vibrancy and opacity on dark garments.
• It’s essentially invisible in the finished print but does most of the visual work.

Why a choke matters

A good underbase is slightly smaller than the colours that sit on top of it — a technique called choking. If the white extended exactly to the edge of every colour, the smallest movement on press would leave a thin white halo around the design. By pulling the underbase in fractionally, the coloured inks always cover it, even with normal press variation. It’s a small detail that separates clean prints from amateur ones.

What halftones are

Screen printing lays down solid ink — it can’t blend colours the way a photo printer can. Halftones are the clever workaround: gradients and tones are broken into tiny dots of varying size. Large dots packed closely read as a solid colour; small, widely spaced dots read as a lighter tone. Step back and your eye blends them into a smooth gradient, even though every dot is the same solid ink.

• A dark area uses large dots; a light area uses small dots; the dots themselves are 100% ink.
• Halftones let you fade one colour to nothing, or simulate shadows and highlights, without extra inks.
• They’re measured in LPI (lines per inch) — higher LPI means finer dots and smoother gradients but is harder to hold.
• They’re the foundation of photographic and “simulated process” screen prints.

How LPI and mesh work together

Halftones only print cleanly if the screen mesh can support the dots. Too fine a halftone on too coarse a mesh and the small dots fall through the gaps or clog; the result is lost detail or muddy tones. Matching halftone frequency to mesh count is a core skill, and getting it right is what makes a gradient look smooth rather than blotchy.

1. 1Coarser halftones (lower LPI) are more forgiving and reliable, especially on textured fabrics.
2. 2Finer halftones (higher LPI) capture more detail but demand higher mesh counts and tighter control.
3. 3The mesh must be fine enough to hold the smallest dots without them dropping out.
4. 4On rough or fleecy fabrics, push toward coarser halftones so detail survives the texture.

Putting them together: simulated process

Combine an underbase with halftones across several spot colours and you get “simulated process” printing — the technique behind richly detailed, photographic screen prints on dark garments. The underbase gives every colour its vibrancy; the halftones blend a limited set of inks into what looks like full-colour, continuous-tone artwork. It’s screen printing at its most sophisticated.

“Underbase gives a print its punch; halftones give it its subtlety. Master both and flat ink starts to look photographic.”

What this means for your artwork

You don’t need to build separations yourself, but knowing how these techniques work helps you supply better art and set realistic expectations. Designs with smooth gradients and fine detail are absolutely achievable in screen print — they just rely on halftones and, on dark fabric, a solid underbase. Talk to your printer early about the effect you want so they can plan the separations and mesh accordingly.

• Supply high-resolution art so gradients can be converted to clean halftones.
• Tell your printer the garment colour up front, since it determines whether an underbase is needed.
• For very fine photographic detail, discuss LPI and fabric choice so the result holds up.
• Trust the printer to handle choking, flashing and separations — but understand what they’re doing and why.

These techniques are exactly what turn a simple design into a standout garment, and they reward an experienced press. Velocity Wear handles underbasing, choking, halftones and full simulated-process separations in-house, so your gradients and detail come out clean and vibrant on any garment colour — bulk custom production from a 20-piece minimum, shipped tracked to the UK, USA, Europe and worldwide. Send your artwork for a free quote and we’ll advise how best to reproduce it.