Renewing a finish on a bowl or cutting board
If you want to renew a finish on a bowl or cutting board, I suggest the following:
Wash your item with water and let it dry for at least a few hours.
Light sand any fuzzy wood fibers with 400 or 600 grit sandpaper.
Generously apply a foodsafe oil such as walnut, tung or pure linseed oil for a few minutes with a piece of cloth, until the wood doesn't want to absorb any more oil.
(note that other vegetable oils won't cure and I don't recommend them. A good supplier for finishing oils is Lee Valley Tools)
Wait 5-10 minutes, then wipe off any excess with a fresh cloth.
(IMPORTANT: Don't bunch and throw oily rag away as it can catch fire spontaneously. Open it and let it dry before throwing it out.)
Extra tip: You can melt about 10% beeswax with your oil in a double-boiler to give it an extra sheen. In that case, buff hard with a cotton cloth after 24 hours to remove any excess wax on the wood surface.