I came across this thread on 24 Hr Campfire on using Penetrol. I'd heard of it but never used it. The last post (as of a few minutes ago) gives the history:
The pics in the thread look pretty good, although he doesn't say whether he's followed it up with another finish. Seems not. One guy suggested using it with linseed oil.
Penetrol is a product I've used for thirty plus years and it's not what many people think it is. First it's not a thinner but a paint conditioner that was targeted toward high end brush applicators wanting a 'wet edge' extender. It essentially acted like ball bearings for brush painters looking for better flow and handling. But Penetrol was also a great rust inhibitor used primarily in Europe where the fishing fleets bought it as ' Floetrol" which the Flood Company marketed under that name. My wife was able to run some lab tests on this product back in the 80's using mass spectrometry and found high levels of fish oil. On rusty metal it's a great product that seals and retards further wastage by sealing off oxygen and moisture. I've used it on everything from snowplow frames to you name it. And finally it is a product that will penetrate, cure and stabilize most woods short of the most highly resinous tropicals. I can not see any downside to using this product with wood stocks.
The pics in the thread look pretty good, although he doesn't say whether he's followed it up with another finish. Seems not. One guy suggested using it with linseed oil.