Oil finishes
can provide a high degree of protection for wood with proper application. There are many oil types and brands that can be used to build up hard, glossy finishes that act the same as varnishes. "Polymerization" is a chemical process by which a natural oil (tung, linseed, etc.) is heated to burn off solvent components. When applied properly these oils harden and develop skins. The more oil that is applied, the deeper and richer the finish becomes. At some point, when enough of a skin is developed, the resulting topcoating can be polished using a wax compatible with the finish.
If you want to see some ultimate examples of this type of finish go to the Musical Instrument Makers Forum at
www.mimf.com and get into the gallery of instruments. There are some incredible "oil only" finishes that are virtually indistinguishable from lacquer and poly coatings. Some very nice instruments like mandolins and archtop guitars are illustrated here with deep, shiny, finishes that enhance their look, tone and protect the wood as well.