Shadow marks or shell marks

1. Reduce moisture content of sheet entering press section.
2. Change worn felts.
3. Reduce refining if stock is too slow.
4. Reduce specific nip pressure and/or vacuum on press.
— increase plain press or smoothing press loading.
5. Make certain weave and weight of felt is suitable for grade being run.
6. Check and equalize front and back press loading.
7. Check hardness of suction press roll cover.
8. Check for cupped suction roll holes that cause fibers to rearrange in areas of highest water content.
9. Plain smoothing press may minimize marking until scheduled mechanical change is made.
10. Countersinking on the couch shell can cause shadow marks.