There are two "true" oils used in finishing. One is linseed oil which comes from flax seeds. The second is tung oil Which comes from a nut tree that originally grew in China. Both are called drying oils although neither really fully dries and becomes hard. The primary use of both is in manufacturing oil based finishes.
A product that is a true tung oil will have a label that says either "pure" or "100%". If it doesn't say that on the label, IT ISN'T TRUE TUNG OIL. Forget about all the other baloney and look for one of those two words if you want to use a true tung oil. If the label contains any other chemicals, except a thinner, you are not getting a true tung oil. Real tung oil has acquired a cachet in the past twenty years that seems to elevate it to some type of magic potion. In fact, as a finish, it does not offer anything much different than linseed oil. In spite of the hype, is not significantly more water resistant than linseed oil--both are lousy--nor is it any more durable. Used alone both are fairly inferior "finishes". About the only difference is that tung oil is slightly less amber than linseed oil but it also is slightly less effective at "popping" the grain. By most measures, it is not significantly different from linseed oil.
"Tung Oil Finish" is a marketing expression for products that the manufacturer thinks will give you a finish like the finish you get from a true tung oil. These "Tung Oil Finishes" may or may not contain some true tung oil, but most do not contain any true tung oil. Their only claim to the use of the word "tung" is that it claims to give you the appearence of finish that results from true tung oil. You're buying a "faux tung oil finish".
There are two types of "tung oil finishes". One is mixture of varnish, boiled linseed oil and mineral spirits (called an oil/varnish). The exact mixtures are proprietary but 1/3, 1/3, and 1/3 will get you real close. Some manufacturers add a dollop of drier to speed up the drying. This same mixture is frequently also called "Danish Oil" because it gives a finish that resembles the finish used on much of the "danish style" teak furniture imported in the 50's and 60's. It closely mimics a true oil finish but the addition of the varnish resins gives it more durability and protection. These finishes do not need to be overcoated with a film finish. When you do so, you are destroying the look and feel of the finish.
Here are some oil/varnish mixtures
*)
Deft Danish Oil
General Finishes' Sealacell
Behlen Danish Oil
Maloof Finish (contains pure tung oil and linseed oil)
Behr Scandinavian Tung Oil Finish
Minwax Tung Oil Finish
Minwax Antique Oil Finish
Velvit Oil
Watco Danish Oil
Liberon Finishing Oil ((contains pure tung oil and linseed oil)
McCloskey Tung Oil Finish (contains pure tung oil, no linseed oil)
The second "tung oil finish" is one made from varnish and mineral spirits. The approximate ratio is 1:1. This is really just a thinned varnish just like the stuff sold as "wiping varnish". When one two or three coats are applied, it also mimics the finish produced by a true oil but it is harder than the oil/varnish above because it does not have as much oil. It is slightly more protective than the oil/varnish type or tung oil finish. For all intents and purposes it is a varnish finish.
Here are some thinned varnishes
*)
Minway Wiping Varnish
Watco Wiping Varnish
Formby's Tung Oil Finish
Zar Wipe-on Tung Oil
Val-Oil
Hope's Tung Oil Varnish
Gillespie Tung Oil
Waterlox Original Sealer/Finish
General Finishes' Arm R Seal
Jasco Tung Oil
(*) Courtesy Bob Flexner and some personal information.
One way to tell whether the product is an oil/varnish or a wiping varnish is to read the application instuctions. Oil/varnishes are applied, then given some time to set, then wiped dry. Wiping varnish products are wiped on an left to dry (no wiping off).
Finally, I'm not disparaging any of these products. In fact, they are a more protective and durable finish than any pure oil finish. They are what they are and can give you a very nice close-to-the-wood finish when properly applied and not overcoated with a film finish. My issue is the use of "tung oil" as only a marketing ploy rather than correctly labelling the product.