DWFII said:
From a purely practical point of view, I think there's only one way to resolve this issue...someone should do a controlled study. It doesn't have to involve scientific instruments and clean lab conditions...simply turn a number of bowls blanks from various woods and turn them in pairs in roughly identical sizes and shapes. Soak one of each pair in alcohol, don't soak the other. Compare results.
I have done just this. Soaks in tagged (dyed) alcohol reveal the minimum penetration reported by others. Dry times of soaked - tagged or untagged - pieces have shown no benefit to the soak. The tests were conducted on cubes cut from the same length of wood, and distortion was as predicted by the percentages listed for the wood under test for the dimension and grain direction on both soaked and unsoaked pieces.
Cubes were chosen because they are
controlled shapes, something unobtainable with turnings, and allow easy measurement.
I invite you to do the same, in full confidence of similar results. I have seen only subjective opinions from proponents or soaking. Since the presumptions of the action of alcohol are demonstrably incorrect - as no replacement, displacement or bonding (as in dehydration with H2SO4) is possible with what is as close to an ideal mixture of liquids as can be found, we must conclude that dehydration by dilution is the only possibility. It is, after all, a technique used in other disciplines. It is also done with long soaks and continued replacement of the alcohol to remove
unbound water. While withholding my opinion on the virtues of Aggies, the following might be of interest :
http://nautarch.tamu.edu/class/anth605/File6.htm
This is not the method used for turnings, and, as indicated, it requires the pieces be dried after dehydration because the bound water - loss of which causes shrinkage - must still be removed.
The kind folks at Madison have done a lot of work determining just how and where wood holds water, and the means by which the loss of water produces shrinkage, all we have to do is relate this to the evidence of the ruler.
My Recommendations:
Cutting blanks thinner than the "10% rule," while not allowing for much design modification after drying, allows for more rapid loss of water. Since all shrinkage, as with politics, is local, it is continuous sections which determine the total dimensional change. The diagrams in the FPL documents are an accurate predictor of direction, with the shrinkage tables an accurate source for the percentage. Use this information if you want to minimize drying time.
Relative humidity determines the amount of moisture within a sample, and control of relative humidity is the means to minimize drying degrade. Tenting, which creates a layer of still air of higher relative humidity around a damp piece is a good way to control moisture loss so that the surface will be held at the FSP until the interior has given up its moisture. Paper, which adsorbs water as its parent - wood - does, is perhaps the best choice, as it also re-releases the moisture to the outside atmosphere as plastic cannot. Other means of contolling RH, including doing nothing, in a humid area, work as well.
Finally, the 1" per year "rule" so often repeated, should be scrapped as it relates to turnings, and is predominantly bunk even when referring to planks. End grain loses moisture at 10-15 times the rate of face grain, and cross-grain turnings seldom have any point more than an inch or so away from the end-grain/atmospheric interface, so a turning will dry at a rate much higher than the "rule," which also includes a winter outdoors. Look at the end of any log in your firewood stack to find out just how fast it can dry.
Is alcohol going to dry your wood? Nope. Air has, does, and will.
I don't expect this to gain acceptance the way a new magic formula, tool or grind will. It's certainly not as exciting as attempting to pile on contempt when I ask that those who reference osmosis read and discover that you can drive the molecular equivalent of a 747 through the pores of a wood like maple, much less walnut. Or where someone reads a resume as a purported rebuttal to my assertion that mechanical advantage is greater with minimum tool extension over the rest, and no one who has longer handles on their "bowl" gouges or thicker sections on their scrapers to counter just this, or ever felt the increased pressure on their hand as extension over the rest increased, said a word. It's just not what a lot of folks want to hear, regardless.