Stuart,
Sorry it was Intergrain, not FW's Tung Oil Finish (and these are all Orica as is Cabots and Dulux). The name Tung Oil Finish is misleading (perhaps a bit deliberately so), because it is not raw tung oil as the name seems to suggest, it is a varnish, made by modifying tung oil; all varnishes are made this way, by modding a vegetable oil by chemically bonding a resin to the oil molecule. The type of oil is less important that the amount of oil; the Tung Oil Finish is 70% modded tung oil and 30% resins, and called a long oil. Danish oils are perhaps 75% oil (called a very long oil). The amount of oil determines the flexibility - the more resin, the harder.
I called my concoction a Danish oil immodestly because it aint strictly speaking. But that is how I used it.
I added raw tung oil (Organoil) to increase the working time, and this seemed to have worked well. It may also have been the large amount of thinning agent I added that lengthened the working time. I phoned the Orica help line and asked if I could mix in raw tung oil with the Tung Oil Finish and the guy said yes.
So, to get back to your question, there is 50% varnish in my concoction, 40% thinners and 10% raw oil. From that point of view there is no problem.
The percentage of solids in a mix is apparently also important. By adding all that thinners in my mix, the percentage solids went down drastically. I don't know what effect that has. But a month later I am still greatly happy with my result.
Here is a great link about varnishes: http://www.taunton.com/finewoodworking/pages/w00063.asp