Blown-Out Dots

Blown-out dots are highlight dots that never survive to the press. At 55 LPI the halftone cell measures 462 microns across, so a 5% dot is only about 115 microns wide, roughly one opening on a 230 mesh. That speck of hardened emulsion has almost no perimeter anchoring it to the threads, so it fails first. Under-exposure leaves emulsion soft on the mesh side and the 3-8% dots rinse straight down the drain during washout. Emulsion over mesh below 10% gives the dot no shoulder, and even a correctly exposed screen sheds highlights around impression 200 as squeegee pressure and wash-up abrade them.

The buyer's version: a gradient meant to fade into the shirt stops at a visible hard edge, like torn paper. On a 500-piece run the first hundred shirts have the fade and the last four hundred don't, which is worse than never having it, because nobody wants a box where the prints disagree with each other. I've pulled a screen mid-run and found the 4% dots simply gone, a clean bald patch in the stencil where the sky used to be.

The fix is stencil discipline, not artwork. Expose with a 21-step wedge and find the time that holds a 3% dot without hardening a 95%. Run dual-cure emulsion at 15-20% over mesh, coat 2/2 with a rounded edge, dry flat and fully, post-expose long runs. Most RIPs will enforce a minimum dot, so spec 3-5% and nothing smaller than the screen can hold ever reaches film.

New printers assume blown-out dots mean the film was too light or the RIP dropped them. Hold the positive up to a light and the dots are usually right there, sharp and dense. The image made it to the film. It just never made it into the emulsion.