Tru-Oil is more forgiving in use than plain linseed or tung oil for the reasons that pisgah states. It has been formulated with dryers and other agents,,probably varnishes and such (I'm certainly so chemist) to get it to dry completely and rather quickly. You can make it look like most any type of finish you want with some practice.
Sometimes high humidity will give problems with drying it though.
You can rub all you want with linseed and all kinds of turp and wax concoctions but never really put a strong waterproof finish on the wood. It can be made to look nice,,, but won't hold up for much.
Plus heavy coats of linseed will darken to almost black over the years as it oxidizes. American Walnut is especially prone to that.
It's decent as a light top coating for low gloss and looks over a strong finish underneath. Makes people feel good about rubbing in that linseed for hours for some reason.
TruOil is quick drying and the solids added to it make for a finish that is glossy and can be built up heavily,,if that's what you want.
Most all the Tung Oil finishes pre mixed on the market are of similar concoction. They use a very small portion of Tung oil in their formulation where finishes like TruOil use a small amt of linseed oil.
True tung oil is a penetrating oil though it will dry quicker than linseed which isn't saying much. Raw linseed can sit for almost ever and never really dry/oxidize.
Boiled linseed (chemical dryers added) does actually dry but takes a while too and is about as far from water proof as you can get.
The US Military went to Tung Oil in about '41 for their M1 stock finish (dip process). A change from the previously used linseed. The linseed oil produced alot of smoke on the M1 during sustained fire as it softened up from the heat.
Drying agents used to be heavy metal compounds like lead in Japan Drier but, like wheel weights and fishing sinkers,, that has all been banned now. I don't know what they use now but they still call it Japan Drier.
I haven't used TruOil in years but when I did I always found that the smallest container I could find was the best. Once it was opened, the remaining contents wouldn't last too awful long before they'd harden over in the bottle.
LinSpeed was another similar product. Don't know if they still make that stuff but they used to sell that in tiny little containers. Just right for putting a very light rubbed out coat over a sanded in finish on a stock. Just enough to give a mellow glow to it. None ever wasted in those little containers. One would be enough for several stocks.
