Emulsion

A blank screen is just mesh stretched over a frame — nothing about it is design-specific until emulsion gets involved. Coat the screen evenly, let it dry in the dark, then expose it under UV light with a film positive laid on top: everywhere light hits, the emulsion cures and hardens into the mesh permanently; everywhere the film's black ink blocked the light, the emulsion stays soft and washes out with water, leaving open mesh in the shape of the artwork. Exposure times run 30 seconds to several minutes depending on emulsion type, coating thickness, and bulb strength.

This is one of the real costs behind a shop's per-color setup fee — every screen needs its own coat, exposure, and washout, and getting it wrong (under- or overexposed, coated unevenly) means redoing the whole screen before a shirt gets printed. Dual-cure emulsions, combining diazo and photopolymer sensitizers, have become the shop standard because they hold up to more press runs and finer detail than older single-cure formulas. We've scrapped underexposed screens mid-run because fine text started washing out under the ink's own moisture.

Pros pick emulsion thickness and coating passes by mesh count and detail level: heavier coats for durability on simple graphics, thinner and more precise coats for halftones and fine line work where buildup would clog detail. Calibrating exposure to the specific emulsion and bulb is routine shop work, usually checked with an exposure calculator strip.

Buyers rarely think about emulsion since it's invisible in the finished shirt, but it's why reprinting an old design isn't instant — unless a shop kept the exact screen, burning it again from the film positive is a real step, not a five-minute reprint.