"Seasoned" Wood: What Does That Mean?

A brief discussion of wood drying vernacular, lightly salted with science and pan-blackened. April 24, 2014

Question (WOODWEB Member) :
I have always disliked this term for wood because I think its slang use is very misleading, especially within the luthier community because they insist dry wood still needs to be set aside for years to properly seasoned. What is the difference between "seasoning" and "drying"? I assert "seasoning" is a myth, but it's a topic without much history at least that I can find.

Forum Responses
(Sawing and Drying Forum)
From contributor T:
Yeah, it's a loose term and depends on where you’re from and how old you are. You have "seasoned" firewood that's usually air dried for six months or longer since cutting. But I've always heard our "seasoned" is when it's been AD to our (depends where you live) balanced humidity usually averaging 15% MC across the USA. The usual rule of thumb is one year to an inch thickness, but I'd like to be updated and corrected via the lutherian people.

From Gene Wengert, forum technical advisor:
For many years without kilns, drying was called seasoning. In the early literature on kiln drying, we still see the term seasoning, especially in reference to air drying. It was still sometimes found in the 1950s, but seems to have been dropped after that time. Some people that like to hold wood for a long time call it seasoning or conditioning. I have also seen it called tempering. There are probably some other names too.

From the original questioner:
I'm aware of the slang use of it, I guess I didn't really ask the question very well. I think you answered it anyway Doc but let me take another stab. Luthiers seem to be the most ardent that drying is not the same as seasoning. I simply cannot separate the two since in my mind it's all about MC. If wood had been dried down to let's say 6% and there's no internal stress left, will allowing the wood to sit for ten years (in a hypothetical constant RH) give it some additional characteristic that it wouldn't have if it were used to make a violin right out of the kiln? I mean, isn't 6% still 6% no matter if it's now or ten years down the road? Is this notion of seasoning just a holdover from centuries past when luthiers didn't have access to high tech kilns and optimal kiln schedules, etc.?

From Gene Wengert, forum technical advisor:
We know that white oak, if air dried for two years seems to develop a vanilla odor and the tannic acid is reduced substantially. So, this one situation does indeed have something going on due to exposure to rain, and maybe some fungal activity too. We also know that some components with the heartwood of the wood are water soluble, so it might be expected that with long time wetting, some of these will wash out. We know that it is more than time, as this change would occur in the instrument or other item over time. So, it seems to involve water.

Does long time drying change the sound or, more precisely, improve it? This is not totally clear to me, as you cannot compare old instruments to todays, as the wood is different, adhesives are different, and so on. If stress itself were important, I am sure that we could develop some construction techniques to enhance stresses. So, I do believe that we are likely looking at chemical changes and not stress.

From contributor Y:
While we are discussing seasoned wood, I have heard that air dried walnut lumber has better color than KD walnut. Is this true?

From Gene Wengert, forum technical advisor:
Regarding walnut color and maple too; The color is partially an oxidation reaction that takes time. Heat makes it go faster. Light helps the outer 1/100". So, rapid kiln drying generally develops lighter colors, which we like in maple and ash, but not walnut. The colors will darken with time and light exposure. Sometimes walnut is steamed and the heat and moisture help develop darker colors (true for almost any species). It also helps the sapwood darken.

Special note: Sometimes lumber is partially air dried, getting a dark color on the outside, but then is put into the kiln, where the fast, hot drying creates a light colored core. So, the finished wood has two colors that are obvious.