Coatings and Varnishes
Coatings are applied for two reasons: for special visual effects or to protect ink from scuffing or rubbing off. There are three general categories of coatings in print:
Aqueous coatings are water-based coatings. They’re applied on-press, and cover the press sheet uniformly with gloss, matte, satin, or dull finishes. They behave best on coated or matte stocks, since the inherent coating on such stocks provides an even surface and consistent absorption. Aqueous coatings can be applied to uncoated stock, but there is the risk of mottling due to the nonuniform surface of uncoated stock. Aqueous coatings actually provide better scuffing protection than varnishes.
Ultraviolet (UV) coatings are cured by UV light for quick drying. Available in matte, dull, satin, and gloss, they can be applied inline on a specially equipped press and can also be applied by silkscreen (which costs more because it’s applied by separate equipment after the paper has been printed, but can achieve higher gloss).
Varnishes are also applied on-press (either as the last ink or in a second pass through the press), and are also available in the standard assortment of gloss, dull, satin, and matte. Varnishes are usually applied overall, but special effects can be obtained by using spot varnishes to highlight artwork. Spot-gloss varnishes, for example, can highlight artwork to make it stand out from the page, especially on matte stock. Applying a spot-gloss varnish on a square-cut image is fairly painless, but there’s a bit more work involved in spot varnishing silhouetted artwork (Figure 2.20). The separate plate used for a spot varnish is handled like a spot color.
Figure 2.20. Adding a spot varnish can accentuate part of an image, but creating the varnish plate requires some work (you’ll have to imagine that the palm tree is very shiny).
Note that since varnishes and aqueous/UV coatings are sealants, it’s necessary to apply the varnish or other coating as the last pass. Pieces requiring gluing (such as pocket folders or packaging) require spot application of such coatings, since gluing and folding take place after varnish or other coatings are applied. Spot application applies the varnish much like an ink, isolating it to certain areas (rather than applying it as an overall coat), so that glued areas are free of ink and varnish. This allows the glue to adhere correctly.