hickey

In offset printing, a hickey is a small raised mark or line that appears on the printed sheet, caused by a speck of dried ink, paper fiber, or dust stuck to the printing plate or blanket. Unlike the typographic ornament of the same name, this hickey is a defect, not a feature. It repeats on every impression until removed, turning a press run into waste unless caught quickly.

Hickeys come in two main categories. A spot hickey appears as a small dot surrounded by a halo of reduced ink density, typically under 3 millimeters across. A line hickey

Most hickeys originate in the dampening system, where paper fibers slough off, or on the printing plate itself if it has been improperly handled or stored in dusty conditions. Some stem from the fountain solution drying on the blanket overnight. Prevention requires maintaining blanket cleanliness, using filtered water and fresh fountain solution, keeping the pressroom humidity between 40 and 55 percent, and wiping down the plate before mounting. On long runs, periodic blanket cleaning with mild solvent and a soft brush can extend press time before hickeys appear.

When a hickey is spotted, the operator must stop the press, identify the source, and remove the offending particle from the blanket or plate using a soft cloth. Simply wiping the blanket surface usually clears spot hickeys; line hickeys may require closer inspection or gentle blanket de-inking. Restarting the press with a few waste sheets allows the fountain solution to re-wet the plate properly and restore ink film uniformity.

Hickeys are distinct from other press defects: they differ from picking, where the ink film tears and pulls fibers from the paper; from slur, a smudged or doubled image caused by blanket slip; and from strike-through, where ink soaks into the paper. Because hickeys repeat predictably at the same location on every sheet until corrected, they are one of the faster defects to diagnose and cure on a running press.