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Humidity, Again> - Nov/Dec 2003


Sorry, yes. One newsletter each year will discuss the perils of dehydration. 


We sing this song every Autumn because the dehydration damage in instruments is gradual & unnoticeable until it’s well advanced. The unfinished wood on the inside of your instrument absorbs & loses humidity; during the process, the wood swells & shrinks. Small, gradual humidity fluctuations are not a problem; sudden change & prolonged dryness are. ·


Tone wood used in instruments must age for years in a controlled environment to ensure that the wood resists warping. Then, to prevent wood from changing size & shape while they build instruments, luthiers keep humidity in their workshops controlled near 50%. Even in a complete instrument, swelling & shrinking of the wood occurs. 


Spruce & cedar, used in the tops of acoustic instruments, are softer & weaker than woods used for backs & sides (mahogany, koa, maple, walnut, rosewood...). In addition, the sides, are curved & glued onto bracing that makes them even more rigid. So, when the instrument absorbs moisture (humidity >60%), the rigid sides hold the edges of the weak top in place, & the swelling top puffs outward a little. While the instrument is swollen, the strings are higher from the fingerboard & the tone of the instrument is slightly muffled. The condition is not damaging to the instrument. 


In dry conditions (humidity <40%), the sides still hold the top in place. Shrinking away from the sides, the top is in tension, and can crack. When humidity drops suddenly below 40% or descends below 40% an extended period of time, the top of your instrument risks cracking. 


No one warrantees against cracks caused by lack of humidity. If your instrument dries out & cracks, the repair cost comes out of your pocket. And, depending on the size, location & character of the crack (or cracks), the repair can be pretty pricey– sometimes hundreds of dollars. To add insult to injury, the cracks are sometimes very difficult to fix & evidence of them often remains visible after repair, especially if the wood has time to distort or collect dirt before repair. 


Someone will surely tell you that they’ve had instruments for years, never humidified, & have had no problems. We celebrate that good fortune, but repair several cracked instruments every winter. We keep humidity at Meadowood & at home at a minimum of 40% & strongly encourage you to do so. The rewards greatly outweigh the effort. 


What can I do?

Use humidity meters: where you store your instruments (many people who thought their homes were OK, found out that they were at 20-30% or worse when they actually measured humidity). Digital hygrometers in the $20-$50 range are more sensitive & accurate than analog meters in the same price range. 

In humid periods: (above 60%) you can improve instruments’ voices and playability if you 1) air-condition, 2) have a qualified repair technician perform seasonal adjustments if action gets high. 

In dry periods: (below 40%) you can 1) keep instruments away from heaters, 2) use humidifiers in the storage room or specially designed instrument humidifier to keep humidity above 40%. 

Immediately repair cracks to increase the possibility of complete repair that is less visible. 

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