Pinholes

Substrate is poor or marginally treated

Check and adjust treatment level or change stocks

Surface of substrate has holes

Check substrate and reduce ink viscosity for better wetting. Consult your substrate supplier

Surface tension of ink is not low enough to properly flow out on substrate. (Seen mostly in aqueous inks.)

Reduce surface tension of inks by adding wetting agents

Impression between plate and substrate is too low

Increase plate impression and check print appearance

Sticky-back tape is too soft

Use hard tape for solid print areas when possible

Ink is drying too fast

Add slower drying solvents

Dried ink, dirt or rust is on impression cylinder

Check and clean cylinder/drum

Use of defoamer in water inks is excessive

Add fresh ink or check formula and reformulate ink

Anilox worn

Replace or mechanically clean