It appears that The true oil that you buy is a little on the thick and old side. Is there a home made recipe that you could mix up yourself for a fresh batch?

Tru-Oil is a fine product, designed to be worked-in/applied that way - thick.
Only a very small drop should be applied at one time, rubbed in & expanded with the rubbing to an area the size of a dollar bill.
The heat of the rubbing causes it to thin out and flow into the wood pores.
After one area's rubbed "squeaky", the another drop is used to start on an adjacent area, etc, until the stock has one/more coat(s).

I do, however, artificially thin some Tru-Oil - for brushing into checkering - with mineral spirits, which is also handy for cleaning the fingertips after the rubbing-in.

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Any good spar varnish with good oil will make a dandy finish, much like Tru-Oil.

When Tru-Oil get thick it is time to use it where it does not matter... I would never use thick Tru-Oil on a stock. It starts out nearly water-thin.
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Stock finishing recipe (if you're a glutton for punishment, otherwise, Arm-R-Seal is outstanding)
This is what I have used many times in the past when it was more important to brag I made my own stock oil mix than get results....
60% tung oil
30% boiled linseed oil
10% mineral spirits
and enough drops of japan drier to turn it a weak tea color.
Experimentation is needed to get it perfect, but more or less, its a starting point, more mineral spirits for initial deep soaking, even naphtha (sp?) will get it to soak in deeply....otherwise, ARM-R-SEAL, it has urethane solids in it to make the process go faster.

....hmmm, just had an idea...what are urethane solids and can they be had singularly to create a pore filling mix....

Sitka Deer:

Would you mix the spar varnish and oil, or would it be best to apply several coats of varnish and then the oil on top of the varnish?

You said a good oil. I don't know much about oil. What would you suggest?

Minwax Tung Oil Finish sold at Home Depot or Lowes is much better.

Pure tung oil (NOT tung oil "finish") mixed with a high solids spar varnish, cut with mineral spirits. Ratios are roughly equal- I used to carefully measure, now I just eyeball it (detecting no difference in effect). Components are a bit pricey but like everything else you get what you pay for, and it goes along way.

With any home brew, mix only what you need for that project. Tiny amounts. If it thickens up on you the molecules have cross-linked and effectiveness is greatly reduced. (Any chemists out there feel free to correct me. Could also be polymerization? Dunno, just that personal experience taught me a lesson in that regard.) I do save the thickened stuff and use it for finishing some wooden projects for the labs in the college I work for. I wouldn't rely on it for use on a gunstock that will see real-world usage out in the weather. Hell, I don't like an oil finish for that application anyway! But that has already been discussed, and I'm sure will be again!

gnoahhh is exactly right, though I tend to use quite a bit less solvent. Cross-linking and polymerization are actually the same thing; Monomers become polymers by cross-linking.

All oil "finishes" are a combination of oils, resins, waxes and solvents. The idea in almost all home-user products is to make them easy to apply, not better finish.

There is no difference between tung oil and linseed and they are interchanged without concern in commercial finishes, including finishes specified as "Tung Oil Finish". Marketing is the only reason we know the difference between them... or rather that tung oil exists. It tends to be treated better during manufacturing and because it is easier to keep "clean" it is more often a better product. Which is why it often costs more when pure and fresh.
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