Tung oil will polymerize if in contact with air, if no air contact it will keep forever (kind of) in a partial filled can there is only a relative small amount of oxygen present that can react with the oil.
Opening and closing the can every time some is used will of course bring new air/oxygen into he container, if you have a container that you can close and open reliable then adding things like glass marbles or water to keep the container full is the way to go.
The problem (or not) is that the polymerizing can not be undone, as with some finishes adding a thinner will bring it back to original, however if your Tung is only a little thickened it probably can still be used by thinning it with terpentine.
I use a re-closable glass bottle and add water to keep the bottle full, it stays in perfect condition that way and I am able to use it to the last drop.
As for General Salad Bowl Finish, there isn’t much more than hazardous thinners and Urethane oil in it, though it is hard to get any hard info on it, they will not spell out the amount of the thinners but give it 30 to 60 procent, so if we take the halfway point it would be 90 procent, so for what you really get, it is some expensive thinners and a bit of varnish.
2 parts of the MSDS sheets with me adding the urethane as an ingredient in between.
I recently received an article, which I'm going to assume from aaw or fine woodworking in mailbox.,it was about professional quality woodturning finishes. A mix of tung oil, poly and oderless thinner. Put on with a red pad. Didn't save as was in mailbox but now can't find. Did anyone else recall seeing a recipe for this finish and application techniques. 
