378Canuck
There are whole lot of books written on drying stock wood and none cover the gamut! It is easy to ruin a blank and most do it by drying the wood too rapidly.
Highly-figured areas and end grain are waxed to slow the drying in those areas. If you think of wood as a bundle of very small straws it is easy to visualize the water leaving those areas rapidly. When wood gets to about 35% moisture content (fiber saturation point) it starts to shrink as it dries. Before that the water loss was unbound water loose in the cells and various vessels. The bound water in the cellulose walls holds the wood in a plumped up state.
When the wood is dried too fast the outside dries and can surface check because it shrinks faster than the inside. But worse than that if the surface gets down to about 6% while the inside is still quite wet the surface wood will take a set. It will not shrink much beyond that stretched size.
When the middle dries it will shrink to much smaller than the outside. The internal wood can literally be pulled apart by the "case-hardened" exterior. The damage is usually called collapse or honeycomb.
When looking at blanks lay a straightedge across the grain on one side. If there is a big valley there (especially if there is another just like it on the other side)it is probably a worthless blank. Many sellers plane the outside of their blanks and round the corners. They give all kinds of reasons that sound better than hiding case-hardening...
Kiln drying is never done to produce better wood. It is only done to dry wood faster "with an acceptable level of degrade." Mills cannot afford to stockpile lumber while they wait on it to dry. Getting it out the door is important.
Not everyone agrees on all aspects of drying lumber and MC is just one issue. It is fact that 6% is a point where wood takes a set and reduces the amount of future moving it will do. The more times it cycles down to 6% the more stable the wood will be in service. Most custom stock guys will not consider wood less than 5 years dry and many insist on 10. All prefer old wood.
That said, many use wood all the way up to 12% because that is what it will be after laying around in their shop in the summer. WInter is when the humidity tends to cycle low in most places and do the serious drying for a set. Obviously there are lots of parts of the country that get wetter in the winter and I am talking about indoors with central heat.
Getting the water out rapidly in the beginning and slowing it down when fiber saturation point is neared and then speeding it up again once the wood has done most of its shrinking and is only working on a set is key to making good stock wood as fast as possible.
The rule of thumb about drying for one year per inch of thickness really misses the big issue of low-end cycling. It is a very good idea to stack dry blanks in a wetter area and then bring them back into a very dry area repeatedly if you intend to rush the project. Get it very dry several times over the course of a year and you will likely have wood as good as much older...
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