For as long as I can remember, I've generally relied on a satin polyurethane spray for wood finishes. But reading about tung oil and how it makes the grain "pop" (technical term is chatoyancy) I was curious to try it, despite my hesitancy about its overall durability compared to urethane or lacquer.
I started out with 100% pure tung oil, thinned 50% with spirits and applied by hand. Originally I didn't care about building a sheen. I'm not sure why I became kinda obsessed with it, maybe because the wet look of the tung oil was so hypnotizing, and when it dried the contrasting flatness could not compete.
So halfway through I started blending in glossy spar urethane with the oil to try and build a slight satin sheen. That sort of worked as the glossiness set in the pores and in some of the grain, but altogether it was uneven.
Against my better judgement I kept fiddling to try and even things out. I applied pure oil which flattened everything too much, then tried to reapply the blend which ended up streaking again. Finally I decided to put a coat of spar urethane and end things once and for all. It turned out super glossy, which I didn't want initially, but at least it is even and now super tough. If I decide I don't like the gloss in the future I can sand down to the oil finish and try building it back up or try buffing the oil with wax (the right way to get that soft satin sheen).
Raw, no finish (click to enlarge):
After about 2 coats of tung oil:
About 3 coats of 33/33/33 blend, a few minutes after application (deceptive as it is still wet)
Final product, dry, glossy because of the spar urethane
Overall I'm happy with it and looking forward to putting it all together and playing it as part of a kit!
-- NOTES for the future and more details --
Approximate breakdown of steps (min. 24 hours between coats)
1 sand 320 grit, 50/50 pure tung/mineral spirits
2 sand 320 grit, 50/50 pure tung/mineral spirits
3 sand 320 grit, 50/50 pure tung/mineral spirits
4 sand 400 grit, 50/50 pure tung/mineral spirits
5 sand 400 grit, 50/50 pure tung/mineral spirits
6 sand 400 grit, 50/50 pure tung/mineral spirits
7 sand 600 grit, 50/50 pure tung/mineral spirits
8 sand 600 grit, 33/33/33 pure tung/spar urethane/mineral spirits
9 sand 600 grit, 33/33/33 pure tung/spar urethane/mineral spirits
10 sand 800 grit, 33/33/33 pure tung/spar urethane/mineral spirits
11 sand 800 grit, 33/33/33 pure tung/spar urethane/mineral spirits
12 sand 800 grit, 33/33/33 pure tung/spar urethane/mineral spirits
13 sand 800 grit, 100% pure tung oil
14 sand 800 grit, 20/20/60 pure tung/spar urethane/mineral spirits
15 sand 800 grit, 10/40/50 pure tung/spar urethane/mineral spirits
16 touch up with spar urethane to even out the finish
Thinning with mineral spirits allows you to wipe-on the finish as the mineral spirits evaporates cleanly leaving only the oil/urethane that then cures. I used shop towels, linen cloths, and sometimes just my finger to wipe it on. In the future I think I'd like to replace MS with citrus solvent or low odor MS because that stuff stinks.
Keep the finish formula consistent throughout the process so things stay predictable. Switching the formula or finish half way through is not a good idea. Also be consistent with sanding - sometimes I would sand and tack, othertimes I'd sand and leave the dust, other times I'd try and wet sand.
Plan ahead how many coats you want and know when to stop and walk away! The most dangerous thing to do with finishes is to over do it. Always easy to add, very hard to subtract.
For the inside I did 3 coats of tung and 1 coat of oil/urethane for the inside, ~400 grit sanding between coats.