i cant find an answer for this doing a web search, i found you want you keep your wood from drying out, and a lot use linseed oil to protect the finish, im wondering what happens if you spray an extremely light coat inside the guitar? i know linseed oil is a great wood conditioner and works better as wood ages, i wonder why i cant find any info on doing on the body interior? john
You keep your guitar from drying out by keeping it in a properly humidified environment(40-50%). Coating the inside with linseed oil doesn't sound like a great idea to me, could dampen the sound. No reason to put linseed oil on the outside either since it likely has some type of finish(lacquer probably). Wiping it down with a soft, dry, lint-free cloth works well. I use a soft microfibre cloth. Linseed would be OK for the fretboard but you'll only want to leave it on for a few minutes and then wipe off the excess.
Guitar finishing is a paradox. For preparing wooden items for maximum stability with respect to both size and not warping, they should be finished identically on both sides.

However, that stability would be very much at the expense of resonance.

I believe that tung, not linseed oil is used in some cases as an outer finish for a guitar. But never as a inner finish.

Wood for guitar construction is stack dried over a period of months, and is acclimated to the expected 40% RH and 70 something temperatures that would be present in ideal, (read "museum"), storage.

Outer finish is a contentious topic at best, with the most traditional and vehement supporters being of the opinion that old fashioned nitrocellulose lacquer is the ideal finishing material. The finishing material in most Asian brands or point of manufacture is either polyester or polyurethane, which is scorned by anybody who thinks that a guitar's headstock has to say, "Gibson", to be worth anything.

But here again, whatever the finishing material, it is only applied to the guitar's outer surfaces.

Here is an ancient technique still used in instruments today: http://en.wikipedia.org/wiki/French_polish

Multiple finishing options shown here: http://www.lmii.com/finishing-options

Or, you could simply read this sticky about maintaining proper humidity for your already finished as much as it should be guitar: https://www.ultimate-guitar.com/forum/showthread.php?t=987641

As rohash already pointed out, proper humidity levels in the guitar's native habitat, will work miracles in extending its lifespan.
Last edited by Captaincranky at Jan 12, 2015,