Should I worry about humidity? - Nov 2000
As an owner of acoustic instruments, you should worry about large, drastic humidity changes. While the outside of your instrument is finished to protect against moisture and dirt, the inside is not. In humid conditions, unfinished surface absorbs water and the wood swells. In dry conditions, the wood loses water and shrinks. While small, gradual fluctuations in humidity should not worry you, large, sudden changes and prolonged dryness are genuine cause for concern. Tone wood suppliers carefully select, cut and age woods for a minimum of four years to ensure that the wood is both stable and responsive when used in an instrument. Aged tone woods generally have moisture content between 40% and 60%. And, because wood changes size with moisture content, instrument builders keep humidity in their workshops very stable, typically at 50%. In this way, luthiers ensure that the wood that they shape or glue will not be swollen or shrunken relative to the other wood in the instrument. Relative swelling and shrinking of the wood remains important after the parts are glued together to make an instrument.
What Can I Do?
In humid periods:
keep instruments in air-conditioning,
if air-conditioning isn't possible and you note undesirable changes, take instruments to a repair technician for seasonal adjustments.
In dry periods:
keep instruments away from heaters,
use room- or instrument- humidifiers where you store instruments.
Take instruments that crack for repair immediately to increase the possibility of complete repair.