Author: mschmidt
Date: 2010-11-23 17:41
I find it hard to believe that the temperature coefficient of wood expansion is greater than the humidity coefficient of wood expansion. In other words, I would think that the wood is more subject to stress by changes in humidity than by changes in temperature. If, in fact, oboes tend to crack more in the winter, it's probably not because it's cold outside--it's still room temperature inside, where the instrument is being played. Rather, it's that 50% relative humidity outside at 0 degrees C means that, when that same air is brought indoors and heated, relative humidity will be much lower (10-20%). This means the air will be more drying. The inner bore surface will get to 100% relative humidity when the instrument is played (that's why you get condensation in the bore) and it seems very likely to me that the differential humidity between the inner surface and the outer surface would create the maximum stress on the wood.
Of course, it is also possible that an instrument carried outdoors in a poorly-insulated case might be subject to sudden changes in surface humidity and temperature, and the slowness of water and/or heat transport from the middle of the wood (away from either the inner or outer instrument surfaces) may result in differential expansion/contraction and stress on the wood. But, again, I'd bet money on humidity changes being a more likely factor in cracking than temperature changes. For one thing, the transport of heat in dense grenadilla wood should be several orders of magnitude faster than water transport.
One thing I have never seen is a compilation of cracking statistics. Where was the instrument when it cracked? Was it being played? What was the ambient temperature? What was the ambient humidity? How frequently was the instrument played? How was it swabbed, and how often? Was the bore oiled, and how often? All our musings on this thread are just speculations without any empirical data. I suspect that most incidents of cracking occur in poorly characterized environments, and that misconceptions about the causes of cracks may lead to selective and even erroneous reports of conditions. (There must have been a draft from under the door!) Even with this data, we still might be helpless to reach a solid conclusion about what presents the greatest risks or how to avoid them. Every piece of wood is individual. There may be multiple risks that affect different pieces of wood differently.
I once was trying out a cracked oboe. The owner said that her teacher thought it was a good sign that the oboe cracked, since it meant she (the owner) was finally putting a proper amount of air through the instrument. This is really the most ridiculous explanation I have ever heard, and makes hardly a whit of physical sense. But it was stated by a professional oboist, so it must be right, even though the education of a professional oboist probably involves a minimum of physics and chemistry! I am afraid that the cracking of oboes is another one of those minefields for musicians--a situation in which even the best physical scientists would have a hard time sorting out all the variables, but where the hapless musician, in hopes of some sense of regularity and control, is left with nothing but hearsay and myth to guide him or her.
As a scientist, I accept that my oboe may or may not crack, and that I should reasonably protect it from extremes of humidity and temperature. I occasionally oil my bore, just on the idea that I am restoring some plasticizers that the wood may lose through oxidation or leaching (that drip down the back of the bore). But I know I have no idea whether I am doing any harm or good in my daily practice, and when and if the instrument cracks, I still will not know.
I think the best way to avoid cracks is to buy an instrument that's at least five years old and has no cracks!
Mike
Still an Amateur, but not really middle-aged anymore
Post Edited (2010-11-23 17:44)
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