I have just been making my first guitar over the last few days from scratch and I have just gotten to the point of needing a finish for it. It is a solid body slide guitar. I was wondering if anyone had experience in oiling a whole guitar body instead of varnish. Pros and cons. Any advice? How long between oiling the next time? Any good oils for this?
I have an old guitar (electric) that had a battered finish. I stripped it completely and used linseed oil to refinish it. I don't think it changed the tone in any noticeable way, and its been fine ever since. That was about 40 years ago. Some caveats though:
1) Oil will never give you a really high gloss finish. If that's what you want, use something else. If you want it to look "natural" though, oil is great.
2) It should really be regularly maintained, certainly for the first few months. Oil it and oil it again. Keep going till it stops absorbing any more. As I remember it, the rule was every day for a week, every week for a month, every month for a year.
3) Oil finish hardens inside the wood, not on the surface. For flutes it's great. For acoustic guitars, probably not. As far as I know this has never been the method chosen for finishing soundboards. The traditional finish there would be shellac which seals the surface rather than soaks in, and adds as little weight as possible.
4) As others have pointed out, oil offers little protection from scratches. However it often still looks ok, and the finish can very easily be touched up. The finish will never chip or peel off, because it actually becomes part of the wood.
I would say probably the same way you would use oil on any other piece of wood. I do think that oil is a better way to go than varnish or other types of hard sealant because it inhibits the vibration of the wood when you are playing. Oil will let the wood vibrate naturally and will give a more resonant tone.
While I am not a luthier. My good friend Charles Fox is one of the top luthiers in the US he lacquers his guitars, acoustic and solid bodies. From my limited understanding oil dampens the resonance of the wood while lacquer or French polish accentuate the natural resonance of the wood which enhances tone and sustain in a guitar. This is of course more important in an acoustic guitar. But even in a solid body electric I wouldn't take the chance.