Wooden Instruments vs Humidity, Part 1.

If we learn what sets of conditions really cause our instruments to swell or contract, we can take steps to minimize the danger of cracking or bursting.


Being a scientist at heart, I wanted to know more about what happens when wooden musical instruments are subjected to changes in humidity and temperature. 

If we learn what sets of conditions really cause our instruments to swell or contract, we can take steps to minimize the danger of cracking or bursting.

For years I thought that the absolute humidity (grams of water per cubic meter of air) was the controlling factor in the expansion and shrinkage of wood, but this is incorrect - it is controlled mainly by the Relative Humidity.  Because the equilibrium water content of wood decreases with increasing temperature, the fact that AIR can contain more water at higher temperature does not mean that WOOD does. I will present references to technical literature to back up my conclusions.

In short: radical changes in relative humidity should be avoided. Big temperature changes are not so problematic as long as the relative humidity is about the same at each temperature. Keep it in a case!

Fortunately, wood is “plastic”. This is actually a technical term that means that it will eventually adapt to new conditions by "creeping" or slowly warping so as to reduce some of the stress.  This can be seen in guitar necks where the tension of the strings eventually bends the neck toward the front. Similarly, one will see instruments where the top has dished in between the sound hole and the bridge and dished out between the bridge and the tail - they likely weren't built that way. Creep seems, I think, to happen more quickly across the grain that with the grain.

I will, later, present an analysis that shows that if wood were not “plastic”, wooden instruments might not survive even one change of seasons.