How to Recognize Coated Paper Picking
Picking is when coating or paper fibers are lifted off the paper surface by the ink, usually on the trailing edge side of a solid area, leaving a white spot, with a small strand of lifted fiber often in front of the white spot. It differs from pinholes: pinholes have clean edges and no fiber direction. If picking occurs, reduce viscosity or speed; do not add ink to cover it up.
Picking is when coating or paper fibers are lifted from the paper surface by the ink, usually on the trailing-edge side of a solid, leaving a white spot; often a small length of lifted fiber is in front of the white spot. It is different from a pinhole: a pinhole has clean edges and no fiber direction. When picking occurs, reduce tack or reduce speed; do not add ink to cover it.
Marks on the Paper Surface
Turn the trailing edge of the solid toward the light. A picking white spot is not a round hole but a small piece torn from the paper surface, with fuzzy edges; sometimes you can see coating lifted up. The lifted paper fibers fall onto the next revolution and become a dirty spot, so a string of dirty spots often follows picking. If you only deal with the dirty spots and not the tack, the dirty spots will keep coming back.
Coated paper, ink that is too tacky, and a press speed that is too fast for this paper are the most common set of causes. The same bucket of ink does not pick on uncoated paper but picks when switched to coated paper; the problem is the paper-tack interaction, not the plate.
Distinguish It from Other White Spots
| White spot | Direction | Action |
|---|---|---|
| Fuzzy edges, denser on the trailing edge side | Yes | Reduce tack or reduce speed |
| Clean edges, no fibers | No | Check as a pinhole or void |
| A paper fiber in the center of the white spot | Fiber has already fallen | This is a dirty spot; look back for the earlier picking |
For This Round, Do This First
- Look only at the trailing edge of the solid and check whether any coating has been lifted.
- If so, reduce tack. Do not add ink first.
- If it still picks after reducing tack, reduce speed, and note the speed this paper can tolerate.
