Just to share the info. from the research I've been doing for months on the "penetrating" properties of *all* manner of oils and resins, from tung oil to epoxy and CA glue. The idea here is obviously about improving the hardness and reflective tonal properties of fretless fingerboards, producing liveliness, and/ or compensating for relative dead spots (not those caused by the bolt-on phenomenon). I've been building many fretlesses , all of the Fender Jazz/ P-J type, with many body woods, fingerboards and neck woods. I've been learning a lot, and the more I trust my ears, and use empiricism along with research , the clearer the complicated picture is becoming. The builds sound incredible, but I want to seek perfection on every one. Duh. But the main point here, is, I looked for weeks on the internet, for VALID scientific research on the "penetrating " qualities of al the agents we'd use to make, say, an Indian rosewood board more reflecive, allowing a great growl. (Not that I'm a huge fan of ebony boards on maple, because they can be so bright and have relatively scooped mids). I greatly prefer the sound of Brazilian Rosewood, and similar woods, for a well-balanced, musical interaction with strings re; growl, warmth, fast attack, etc., be those strings great flats (TI JAZZ!) or rounds (TI JAZZ ROUNDS!). OK, here's the scoop; I found ZERO reliable, well-researched proof that ANY oil, or resin/ acrylic/ polyester/ etc., actually penetrates *any* wood. (OK, maybe balsa...) Some might say who cares? Well, to really harden a wood, and blend the hardness deep in, without a thick resin surface on top, would be very nice; Something closer to wood on top, with the density and speed of vibration beneath, creating a more natural, musical tone. Or, to avoid the gummy effect of too much linseed oil. (NOTE: I have not been able to find good reliable info on specialty products like hardened wood...can't tell if they're malarkey or not, though I feel the idea is the ideal). Just with lets say oils; Here's a link on heated vs unheated linseed oil. The extra step is useless. http://www.woodworkersresource.com/content/should_you_heat_your_linseed_oil_before_applying_it/ Better yet (sorry I can't find the bookmark, is a long article with many top notch luthiers describing the almost non-existant penetrative quality of all the oils we use. You can find it. I've got a cold & am beat tired...This one will really make you skeptical. These guys are not yahoos. I recall names like Sadowsky, Lull, Suhr, etc., in the article; definitely not ******** talk over a beer kind of crap... Lastly, I looked all over in the resins industries for science-based articles proving the effectiveness of pulling epoxies, polyesters, etc., into wood. What I found, time and again, is that the only thing that "penetrates", is the penetrating agent. The resin stays on top! Some boat forums have people in vicious arguments about this, but there's no science to prove any real penetration. All I find singing the praises of "penetrating" resins comes from (surprise!), the *manufacturers* and *sellers* of said products. Enough said about that. The Only thing that I had ANY faith in , was a cement finisher in Los Angeles who just seemed a credible guy. He said that he wouldn't do designer painted cement floors without the use of penetrating agents added to epoxies, because of the huge cost of going back to repair his jobs, and that the added cost (passed on to the client), was worth it. But that's cement, and he could still be wrong. Final statement; don't just buy the idea that ANY oil, or resin, either with the use of some penetrating vehicle or not, is going to drive your hardening agent deep into the wood. The MOST I've seen from big luthiers, smart guys running empirical tests, and even-laughingly so- from marketers of said products, is in the 1-3 mm range. Rather pathetic results. If anyone can point to some GOOD science on this that defies what I've found, I'd love to see it. Frankly, I'd LOVE to be able to drive a hardening agent into , say, Indian rosewood, without a thick coat on top. Again, I think the *concept * of hardened woods, such as we've seen here on TB, is great. The process wherein the resins are supposedly driven into the wood under intense pressure in an autoclave? Sign me up if it works. Cheers.