I've read many posts regarding making your own oil. Turp, linseed oil, pine tar and jap drier seem to be the staple. I saw several recipes which also add varnish. What does varnish bring to the table in the soup recipe? I will be oiling the interior.
I usually buy equal sized containers of linseed oil, turps, and a pint of pine tar. mix it all in an empty paint can, and add a half a bottle of japan drier.
It isn't a precise mixture and doesn't need to be.
I've had old tung oil laying around, some spar varnish, etc.. and even through that stuff in at times. The varnish would just add more oil- the good stuff would have tung oil in it. The turps basically thins out anything else.
As a matter of fact, I had a paint can of turp that I used to store my brushes in. Just the brushes used for varnish. I used the old turp in there as a base for some boat soup once.
The down east boat soup is:
Bolied linseed oil: 1qt
Turpentine: 1qt
Pine Tar: 1/2 pint (though I've used a full pint recently)
Japan Drier: 1/2 pint
More importantly is the wood. White Oak, Meranti, Fir all like to drink up oil well. This I know from experience. Other woods, you'd have to try on your own, or others can chime in.