A condition in offset lithography where the non-printing areas of the plate lose their ability to repel ink. Because the dampening solution fails to keep the background clean, ink transfers to the non-image areas and prints as a light, dirty background tint on the paper. It is usually caused by a lack of fountain solution, improper pH, or an oxidized plate.
Heard on the job
The cyan unit is scumming on the tail edge, so turn up the water slightly and check the fountain solution pH.
Do not mix it up with
- Tint block: A tint block is an intentional solid background color, whereas scumming is an accidental, dirty background tint.