There are many advantages to coating your inkjet prints. Firstly, coatings provide protection from fingerprints, atmospheric pollutants, UV light, moisture, and help provide resistance to scuff marks on prints made with pigment inks.
Further, Wilhelm Imaging, the only real authorities on the issue, indicate that coatings can seriously increase the longevity of your prints, especially a concern with dye based inkjet printers .Another reason to coat prints is to reduce bronzing and gloss differential - in most cases, coating your prints will eliminate all but the most severe problems.
Hahnemuhle Protective Spray is the classic inkjet print coating, suitable for all papers/canvases, except super high gloss papers. It is a very thin coating and essentially invisible.
Hahnemuhle Varnishes are specifically for canvas prints and come in three different coatings, allowing you to choose the type of finish – matte, satin or gloss. These coatings are thicker and visible.