It is a protective layer that increases the durability and aesthetics of your printed piece. You cannot print (ink-jet or by hand), glue, or foil stamp over coatings, so you need to leave an uncoated window if you want to do any of these
There are several types of coating:
- Varnish – Varnish is essentially ink without pigment. It comes in gloss, dull, and satin
- UV Coating – UV Coating is a clear liquid spread over the paper like ink and then cured instantly with ultraviolet light. It can be a gloss or dull coating, and can be used as a spot covering to accent a particular image on the sheet or as an overall (flood) coating. Keep in mind that this thick coating may crack when scored or folded.
- Aqueous – Also known as AQ, is water based. It has better hold-out than varnish and does not crack or scuff easily. Aqueous does, however, cost twice as much as varnish. Aqueous comes in gloss, dull, and satin.