Yeah I was just theorizing with no actual experience.
But it does make sense to me if wood fibers absorb anything, they will swell and weaken but, seems like this would only apply to a wood that the mineral oil would soak in to.
Naturally oily dense woods like olive, cocobola and others probably wouldn't absorb anything, thus not affected. Same with stabilized ones. But this brings up the question as why use it if it doesn't do anything? - or does it.
As for it being inert, does that mean it won't mix with any other substance?
Personally I use rubbing alcohol to clean and remove the outer layer of oil in the wood, let completely dry, them tung oil to seal back up. Might try Bill's suggestion of 25% bleach next time.
I've never understood, or even believed, the premise that absorption of anything liquid into wood inherently weakens it (depending on the specific liquid, obviously). After all, when the wood was still alive and at it's healthiest, it's pores & grain were already holding moisture and/or oils of some kind; and the wood was likely at it's strongest under those healthy conditions.
Water can indirectly ruin wood eventually by dry-rotting, because it fosters the growth of fungi which damages (eats) the wood fiber and therefore weakens it. It's not because the water by itself did any damage, but the biological aftereffects of continuous exposure to water and oxygen is what ruins it. By contrast, mineral oil won't foster such growth of fungi, bacteria or anything else, because it's chemically inert and therefore has no mechanism by which to ruin or weaken the wood. Think of all the kitchenware and utensils like wooden salad bowls & tongs, wooden spoons, cutting boards, etc., that actually depend on the use of food-safe mineral oil to keep them non-absorbent of food contaminants and in good shape after repeated washing over years or decades of time. Makes it kind of obvious it's not doing any damage, and in fact is helping to prevent it.
The inertness of mineral oil is what makes it non-reactive (chemically) with any substance. That's at least part of the basis behind it's use as a preservative for a couple of reasons: because it's absorption into porous material can prevent other harmful liquids (like water) from being absorbed, and because it can also protect a material from oxidation as well. Mineral oil has sometimes even been used as a suspension for medicines for these reasons. The inertness of mineral oil is also why it works as a laxative without toxicity by ingestion, because the body can't absorb it (due to it's inherent non-reactivity), and just passes it on.
The only justifiable gripes I've heard or read of, about mineral oil used on wood, are that it's sometimes incompatible with other wood finishes (like the 'drying oil' finishes previously mentioned, for example). That only means that with some finished wood, mineral oil may not do anything to preserve or protect it, because it can't be properly absorbed by the finished wood (because the finish has sealed it) and just remains at the surface and might leave a messy/gummy surface appearance if applied too often and not cleaned off. Or the flipside, on a piece that's previously been treated with mineral oil only, some other finishes can't properly be absorbed or cured because of the mineral oil's presence in the wood. Even then, it's still doing absolutely nothing to weaken the wood either; it's just a cosmetic issue.
David
