Coatings are among a print producer’s most valuable tools: They protect paper and images from smudging, and can speed the drying process.
Aesthetically, coatings enhance paper finish and/or create contrast between images and background.
Paper stock plays a key role in specifying press coatings and managing expectations. On uncoated stocks, visual effects are secondary to smudge protection. Coated stocks allow both smudge protection and a full range of visual effects. Keep in mind that the same press coating on a gloss, silk, dull or matte stock will perform differently.
Petroleum-based varnish coatings
– Economical overall for perfectly registered spot-coating to highlight all or parts of images.
– Can add a yellow tint, especially over time.
– Effects are significantly greater on dark colors, but barely noticeable on light colors.
– Take a while to dry and spot dull varnish shows after it is dry.
Water-based aqueous coatings
– Faster drying and better rub protection than varnish.
– Spot aqueous exact registration to images is difficult.
– Easily used for spot-coverage, create the glossiest finishes and have the fastest drying time.
– Costliest of the three coatings; often done off-line and off-premise which increases print turnaround time.
Two other techniques that use a combination of dull and gloss coatings
– “The Old Standby”: spot gloss and spot dull varnish coatings registering to each other.
– “Relatively New” Strike-Thru: In a single pass, lay down overall gloss aqueous followed by spot dull varnish. The gloss is absorbed into the strike-thru varnish areas. The technique is most effective on dark ink backgrounds.