For carbon, food prep is the way, but a wooden handle needs to be kept dry after use or you'll never open the knife again!
Never found potato very effective actually. Here's my patina tips: Wash and dry the blade,then remove all traces of oil or finger grease etc with alcohol solvent/lighter fuel e.g. Carbon responds to pears very well, leave the blade in that overnight and the funk starts. Use on citrus fruits particularly,rhubarb, any of the onion family.Quick wash/wipe after each use is all it needs. After a week, Scotchbrite the patina off and get a matte look, put alcohol on and start using again. A week later the patina will be even and tough,after that an wipe with mineral or olive oil once a week will keep all rust at bay,both these are food safe. I got an almost 'Damascus' Tiger stripe look on a CASE cv Swayback after scotchbriting and then leaving it in a lime for an hour, really nice.