Halftone Underbase

A halftone underbase carries the same tonal information as the image above it rather than blocking out the shirt with a flat white slab. The base separation tracks luminosity: near 100% under the brightest highlights, 40-60% through the midtones, and 0-15% under the shadows, where a black garment is already doing the work. It usually runs on 156-200 mesh at the same line count as the color screens, with its angle matched to the top white so the two stack instead of fighting. Screening the base pulls 30-40% of the white ink out of the print.

That missing ink is the entire point for a buyer. A solid base under a six-color sim process gives you a shirt with a plastic card glued to the chest; the halftone underbase version drapes. It also kills the ghost-edge problem, where a shadow that should dissolve into a black tee instead sits on a white rectangle you can find with a fingernail. On dark heather, a screened base is the difference between a print that belongs to the shirt and one that reads as a sticker.

Spec a halftone underbase when the image has real gradation into darkness: sunsets, smoke, portraits, anything with a soft vignette. Choke the base about 0.003 inch so registration drift doesn't show white halos, flash it, and keep base LPI equal to or one step below the top colors. The trade-off is saturation. Less white beneath a midtone means the shirt shows through and the color reads duller, so many separators leave a solid base under heavily colored midtones and screen only the highlight and shadow ends.

Buyers often request a solid white base assuming more white makes a better print. On a photographic design the opposite holds: a solid base flattens the shadow end, adds hand, and puts a hard edge everywhere the artwork was supposed to disappear.