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Green wood has several drawbacks for use in most projects. For the most part all of the wood you purchase is kiln dried. One benefit of kiln drying is the time from forest to manufacture can be a few days (possibly an oversimplification).
Other than reducing the time from forest to construction, does kiln drying have any benefits over natural aging?
I would propose that kiln-dried wood (in particular steam kilning) is sometimes inferior to naturally cured wood.
American Black Walnut is a great example of a wood that suffers when kiln dried. The wood looses tremendous character when it is dried in kilns. The heart-wood and sap-wood boundary is not nearly as vivid in kiln died walnut. This can be considered a benefit if the wood is used in certain commercial situations such as flooring. However in fine woodworking the loss in character is generally not desirable.
Another wood that I have noticed a difference in character between kiln dried and air dried is American Cherry, where the general depth of the color is noticeably muted in kiln dried cherry boards.
Improper kiln drying can lead to some drying defects that may be difficult to see to the unaided or untrained eye. Examples include honeycombing and case-hardening. These during defects usually render the lumber unsuitable for most fine woodworking and can also pose danger when working the wood in certain situations.
The biggest defect from air dried lumber is improper moisture content and perhaps warping due to poor stacking techniques. Problems such as case hardening and honeycombing are not found in air dried lumber.
The difference in color and character between kiln dried wood and air dried wood of the same species is unmistakable for certain species as mentioned above. Walnut and cherry are the most easily distinguished, although I am sure there are others.
Air drying is just plain slow. The general rule of thumb is 1 year + 1 year per inch in thickness.
Properly curing wood usually takes lots of good dry space. For most lumber operations this is a luxury that is tough to justify.
Overall kiln dring is hard to dismiss as a viable way to bring wood to market. Most of the wood I have used over the years was kiln dried and very little of it suffered from any of the drying defects listed above.
However it should be noted that due to the potential loss of character in certain species of wood, air drying should be considered if you are looking to work with these woods or want to highlight the natural character of woods with very dissimilar sap wood and heart wood.
1 year + 1 year per inch in thickness over an inch. Wouldn't that simply equate to 1 year per inch of thickness? :)
Kilns will work fast to dry the wood, in large planks that means that the end-grain will dry out first than the middle. This may lead to cracks.
If you have climate controlled kiln then you can slow the drying down so the center of the wood can equalize before the stress becomes too big.
No, the benefit of kiln drying is speeding up the drying process. Actually most kiln drying (the rapid removal of moisture) actually damages the internal structure of the wood. A slower drying process is better, one that takes multiple days and gives time for the wood to equalize.
