patch

In letterpress printing, a patch is a small piece of paper, card stock, or other material glued to the underside of a printing plate or to the impression surface itself. Its purpose is simple: to raise the height of a specific area so that portion of the plate strikes the paper with greater force, producing a darker or sharper impression where needed.

Patches solve a practical problem. After a plate is locked in the chase and the press is running, you may discover that certain characters or designs print too lightly while others print correctly. Rather than remake the plate or spend time resurfacing it, you can add thickness beneath the weak area. A patch might be a single layer of newsprint, bond paper, or card; for deeper corrections, multiple layers are built up and carefully shaved level with a knife until the impression registers evenly across the entire plate.

The choice of patch material depends on how much height you need and how durable the fix must be. Thin paper works for minor corrections on short runs; card or plastic patches hold up better on long press runs where repeated impression is intense. Patches are always applied to the back of the plate or to the platen, never to the front face where ink rolls, since they must be invisible to the printed result.

Patching is a corrective tool, not a finishing one. It belongs to the pre-press makeready phase, after proofs reveal uneven impression. A well-executed patch is nearly invisible in the final print; a poorly placed or oversized one can create unwanted ghosting or ink transfer. Precision matters: patches must be trimmed cleanly, adhered firmly, and their edges must not create a step that catches the impression roller.

The term reflects the method itself: you are literally patching a defect. Patching sits alongside other makeready techniques like underlaying (building up the entire plate) and overlay work (adding impression to specific spots on the paper side). For modern digital presses, patching has largely vanished, but in shops still running platen or cylinder presses, it remains a quick, cost-effective fix when a plate prints unevenly.