Varnish is a sealer that overprints ink and paper, protecting both from scratches and abrasions.  For design effects, varnish can be used in a variety of ways; gloss, dull, matte, tinted, spot and overall.  Varnishes can make a coated paper glisten or give it a satin sheen.  Varnishes can "pop" a graphic off the page and brighten colors in a photograph.  It can also become a graphic design element of its own.