I spent many years building Ukuleles from scratch. When finishing with tung oil, I would apply the first coat and let it dry, then apply another wet coat and smooth it in with 600 grit wet dry sandpaper while the tung is still wet, making a slurry of tung and sawdust, this fills in some of the open grain of the wood, and helps to make a really smooth finish.

Now, I have repeated this step up to 15 times when finishing my Ukes, really leaves a nice warm looking deep finish on the wood.

After several of the sanded coats, you wipe the last sanded coat off so the surface is clean, apply a final coat of tung oil alone to cure and set on the surface.

With Koa wood it really looks awesome.

good luck

Chuck