The stories surounding Tung Oil are probably part and parsel of some of the
largest urban myths circulating in woodworking today. It was brought into
Europe from the far east and used because it dried harder and was a bit more
water resistant than the boiled linseed oil that the poor old Europeans were
using. Once the poor old europeans developed resin based varnish, they quit
using it. Linseed oil is no longer boiled to crosslink the molecules, but
instead has metalic dryer added to it. Pure tung oil does not and in the
right climate can take days if not weeks to fully cure. Most stuff that is
called tung oil (I.E. Fornbey's) is really wiping varnish that has
polyurethane along with the tung oil. To the wood, oil is oil and it is the
oil that brings out the depth and color of the wood. Having said that,
varnish has oil in it. Its what makes the resulting resin film (be it
traditional phenolic or polyurethane) flexible enough to stay on wood which
we all know moves. Spar varnish is a 'long oil varish' which means it has a
lot of oil in it that results in a flexible film when it cures. It also UV
inhibitors, go figure - outdoors.
In my experience, a first coat of spar urethane thinned about 50% will yeild
the same affect as screwing around with linseed or tung oil. But if you
must, who am I to say.
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