Matt,The BLO does not contribute hardly anything to the CA finish, rather it is used as a catalyst to harden the CA and a lube to smooth it out.
Tung is just like any oil finish: not chemically durable, soft, and does not build a layer of protection on the wood like Waterlox (which is a tung-based urethane) or lacquer.
Below is a submission made to the Yahoo pen turners forum several years back. It is very technical, but Henk is a chemist who understands this stuff better that I ever will:What I meant in my statement about BLO not adding anything to the CA finish was in terms of durability or hardness (which are the two items that Tung has over BLO). Some folks think that BLO somehow hybridizes the CA into a really durable finish (it's difficult to improve on the hardness of regular CA anyhow).