Most NE bowls are not meant to be used as salad bowls or whatever so the range of finishes that one might use is pretty well unlimited. Lacquer, varnish (polyurethane or traditional), shellac, epoxy, penetrating oils, etc are all fair game. Just depends on the effect you're looking for. Without the functional constraints you can just think in terms of film forming or not, shiny or dull, ambering (or colored with dye) or clear, ability to pop figure, repairability, water or solvent based, etc etc. It all works!