Linseed oil is a good wood finish. It's a lousy lubricant. It turns to a gummy, rubbery substance as it oxidizes and "dries." It's actually polymerizing and the dried oil is nearly impossible to remove with solvents, so you don't want it to build up. Walnut oil likewise "dries" by polymerization, not evaporation. None of the fatty oils will evaporate or even boil without decomposition. That's why they're known as "fixed oils." They can't be distilled. Olive oil is unique among the vegetable oils in not exhibiting this drying, gumming behavior. It also isn't a solvent for finish materials, glues or lignin. It's nontoxic and doesn't have an unpleasant odor, nor does it go rancid on wooden surfaces. It's long been used as a finish for wooden items used in contact with food, such as turned wooden salad bowls and cutting boards.
I put it on the fretboard liberally when I start changing the strings, run each new string between a finger and thumb dipped in the oil before I put it on, then when the stringing job's finished wipe it all off with a soft cloth. It leaves just a trace film of oil on the fretboard and strings, but it's enough to make sliding and bending much smoother. The strings last much longer without going "dead" from corrosion and tarnish. I'm sure the numerous commercial products sold as fretboard lubricants and string treatments work as well, but I seriously doubt that any of them work better.

The olive oil doesn't dry out on the fretboard. That's exactly the point. I'm looking for a lubricant, not a finish. The microscopically thin oil coating makes the fretboard and strings noticeably slicker. It would certainly be a silly idea to use it in a French polish as it won't dry. Yes, if you leave a heavy globbed up coating on it, it will attract dirt. If you wipe it off as I do, it won't get dustier than the guitar will anyway, and the dirt wipes off quite easily. And no, the olive oil doesn't get rancid and stink to high heaven. I've been wiping it on my fretboards for years and it hasn't happened yet. I've used it on things like tenor recorder keys for about 15 years with no gumming or rancidity.

I wear daily a vegetable tanned leather belt I made about 3 years ago and oiled heavily with olive oil. No rancid smell yet, it smells like nice leather. Same with leather rifle slings, knife scabbards, etc. (I know we're talking about using it on wood, but the stuff's good on leather, too, where it's also good that it doesn't dry, and it would be a big problem if it produced an offensive odor.) And the spillage on the outside of a bottle that's about 15 years old (this stuff lasts a long time when you're using small quantities) is finally getting a bit sticky on the label, but it doesn't have time to do this on a guitar that's receiving any maintenance or playing. The 15 year old stuff in the bottle doesn't stink (or taste bad), either. Decay bacteria need water to do their thing. If it's kept away, all you get is air oxidation, and the monounsaturated fatty acids that predominate in olive oil don't do much of that. The polyunsaturated acids in the drying oils avidly take up oxygen. BTW, wood finishes made with drying oils will grow a thick crop of mold if stored in a moist environment. I've seen linseed oil finished gunstocks come out of a sealed case white and fuzzy with it. Might be a problem in a humidified guitar case. High humidity might well bring on rancidity of olive oil, as well. Hasn't been a problem for me.

Use whatever you like best, of course. I'm just relaying something that I've found to work well.

By John Culp