I don't remember seeing a recipe to exactly duplicate True-Oil. I believe it's boiled linseed oil, varnish and mineral spirits, but what proportion they use I don't know.
I have successfully made my own similar oil/varnish blend that works very well and have used it on a number of furniture projects as well as my old ash bodied P bass.
I mix equal amounts of boiled linseed oil, varnish (gloss) and Varsol and add a little bit of Japan drier. The first coat soaks into the wood and brings out the grain (wipe of the excess before it sets up). Multiple coats after build up a gloss finish.
Boiled linseed oil, not raw linseed oil is important. For varnish I prefer a traditional varnish, but polyurethane, like Minwax, which is about all you can find these days, works. You can substitute tung oil for the linseed oil if you can find tung oil. Most of the stuff marketed as tung oil doesn't have very much tung oil in it and is an oil/varnish/thinner blend.
You can experiment with the proportions. Less oil and more varnish builds up quicker and dries harder. On warm days I can get two coats on per day.
At any rate you must apply this in thin even coats and wipe off the excess. 20 coats looks very nice on ash. The linseed oil darkens with age. Tung oil doesn't darken as much.
I like making my own and being able to play with the proportions and if you use a lot of it you save money. Other than that I don't think there's much of an advantage over the ready made blends.
