How to Distinguish Water Stains and Dirt Spots
Water stains have soft edges and no particle in the center; after drying, they often become a fainter print mark. Dirt spots are clear white rings with a particle of ink skin, paper fuzz, or dried ink in the center. If the edges are soft, check the water; only when you see a white ring and a particle should you stop the press to remove dirt. Do not call both dirt spots.
Water stains have soft edges and no particles in the center; after drying, they often become a fainter mark. A dirty spot is a clear white ring with a particle of ink skin, paper lint, or dried ink in the center. If the edge is soft, check the water; only when you see a white ring and a particle should you stop the press to remove the dirt. Don't call both dirty spots.
Edge when magnified
A water stain is like a drop of water spreading in the ink; its boundary is unclear, sometimes with a slightly darker ring, but the ring is fuzzy. It is often on the path where the water roller or fountain solution is uneven, and its position drifts across consecutive sheets. The white ring edge of a dirty spot is sharply defined; the particle in the center is still on the plate or blanket, so it appears in the same position on every sheet until it is washed off.
Check again after it dries. A water stain often leaves only a slightly lighter mark, and the white ring will not become a hard edge. The white ring of a dirty spot is still there when dry. This step can prevent you from sending an already dried water stain to plate washing.
Handling is different
| Edge | Center | Position on the next sheet | Action |
|---|---|---|---|
| Soft | No particle | Drifts | Check water volume and water roller |
| Hard white ring | Has a particle | Fixed | Stop and remove that particle |
| Soft, but becomes a hard white ring after drying | Particle appears later | Becomes fixed | First remove it as a dirty spot, then see whether the water brought it up |
Do this first this round
- First look for a particle in the center; don't look at the color depth first.
- If there is no particle, do not stop the press to wipe the plate; check the water first.
- If there is a particle, then stop. After washing it off, print another 20 sheets to confirm that the water hasn't brought up another particle.
