Oil is easy, just a matter of patience. Luckily sanding this is realtively easy (flat top vs arched/carved).
My tips (I do all my instrument projects, as well as other things, in oil - often with stain underneath).
- ignore those saying to use only 'pure' tung oil. It is harder to work with (mostly the viscoscity) and therefore harder to develop that top coating finish you want on a guitar. Use any 'polimerized' tung oil (e.g any that does not explicitly say 'pure' on it - Circa 1850, Minwax Tung & Teak, anything called 'Dannish Oil' etc). You would just have to prep pure oil anyway so save yourself the trouble. The only real need for pure is if finishing a food prep surface such as a salad bowl or cutting board
- remember to raise the grain and do a second fine sanding
- first coat just slap it on there heavy (use a brush). Use elbow grease until it is ALL soaked in (as opposed to wiping off the excess) - friction/heat allow it to penetrate. I prefer a cloth vs a sponge for this part after the initial brush on). The first coat is key to building up a good finish. For successive coats I just use the cloth to both apply and rub in. The most important part that people, ahem, gloss over or skip mentioning altogether in online how-tos I have seen, is the rub in part (it does usually say so on the actual product instructions tho)
- after the 2nd/3rd coat buff lightly (don't strip it) with 0000 steel wool before each additional coat.
- the more the merrier; you can keep going until you get the gloss level (within reason - it's oil not lacquer after all)/surface buildup you desire, but only if you buff in between (or it won't get glossy and will actually start to look bad after additional coats). Like throw a coat on in the morning before work, and another before bed for a week or 2
- if you like a natural finish but want a more robust finish, you can do a single coat of oil to pop the grain and darken the wood, and then go over it with poly (give it a good 48 hours for the oil to cure properly before poly)
edit (forgot): tung oil also makes for a great grain filler - wet sand with it and get a super smooth surface. Even better if you wet sand with it after staining (if staining; you'd need to stain again afterwards, but you fill the grain with stained sawdust).
