Purpose:

1. All dried inks show fingerprints, scuffing and other blemishes from handling, especially in dark solids. Readers can ruin a report cover in only a few minutes. The solution is putting some form of protective coating.
2. Rush jobs cannot allow ink to dry in a short period of time. Adding a layer of coating may be a way to shorten the production time.
3. Designers may use coating for special printing effects.

Varnish

Varnish costs about the same as another ink color and comes in either glossy or dull finishes. It can also be lightly tinted, thereby achieving both color and protection for the cost of one. For a deeply matte effect, print dull varnish over dull ink. Varnish works best on coated papers and may absorb completely into uncoated stock that it neither protects nor beautifies.

Printers either flood or spot varnish. Flood varnishing means covering the whole area; spot varnishing refers to hitting only certain areas, such as photographs.

Aqueous

This very glossy coating you usually see on magazine is an acrylic mixture. It has better holdout than varnish and does not crack or scuff easily. Printers can apply aqueous coating as gloss, dull, or primer, which is very thin.

A printing press can apply aqueous coating inline only when equipped with a special coating unit. As a matter of fact, aqueous costs approximately double the cost of varnish.

UV (Ultraviolet)

For even more protection and sheen than varnish or aqueous, some printers can coat with a plastic that dries under ultraviolet light. These products give tough surfaces for book covers, table tents, and labels for bottle and packaging. You can ask for dull or gloss finishes and flood or spot coverage. Spot coverage will be done using screen printing and yields a thick covering.

Since plastic liquid coating is cured by light instead of heat, they have no solvents to enter the atmosphere. They are, however, sometimes brittle, so they may crack under folding or scoring.