I finish with doctor’s walnut oil/wax bowl finish. The wax is set, or hardened/buffed while spinning to give a nice luster. This is inside and out.
I furnish and also explain to my buyers that owing one of these is not unlike owning cast iron cookware. That after use it should be cleaned minimally, dried and oiled. It’s been reported to me that repeated oiling has deepened the glow, that it’s more beautiful than when they bought it. It only does that help the bowl, but also creates a special relationship with their costly purchase.
I avoid film finishes, except maybe for purely decorative pieces. If it’s a regularly used piece, the film will wear through, and the bowl will go through an awkward period till everything evens out.
Dave, I used to suggest walnut oil to customers till two pieces came back to me. The grocery store walnut oil had hardened on the surface, mostly. Actually it was a sticky mess! I can now attest to the strength of a walnut oil finish. I scrubbed with mineral spirits and steel wool-scrub, rinse, repeat. Fortunately, I was able to remount to the lathe with a vacuum chuck to rebuff and rewax.
It might have been that particular brand, or maybe our climate that added to the problem. Not sure.