Drying wood for musical instruments

      A primer on various lumber drying techniques as they relate to musical instrument construction. 1998.

by Professor Gene Wengert

I am interested in drying woods used in the construction of musical instruments.

I understand that concientious luthiers air-dry their tonewoods from 1-4 years in order to maintain the highest tone quality.

I have heard that in conventional kiln drying they try to achieve certain temperatures in order to "set" the pitch in softwoods for example. Even higher temperatures are required to release the "bound" water in green material.

My question is what takes place with the bound water and pitch in the air drying technique. I am curious about the effects of low temperature drying approaches such as Vacuum, or RF Vacuum.

Drying Methods--Air-Drying vs. Kiln Drying

We know that very slow drying of lumber enhances the musical properties. Drying at warm temperatures or hotter has a definite effect on wood properties. Therefore, air drying for a year and then continued drying in a home or office to achieve the correct final MC is essential. Air-drying alone will reach only 12% MC in most of North America; 7% MC is the typical final MC required for interior uses. We also know that rain on the lumber enhances certain other properties. For example, white oak lumber is normally quite acidic in character. But if you air dry it for 2 years, there is a vanilla odor that becomes very obvious and enhances the flavor of wine and whiskey in barrels made of such material! In short, air drying cannot be replaced for musical instruments--even low temperature systems do not do as good a job.

Bound and Free Water
Now, let's discuss "bound water." In the living tree, the wood cells, which are like skinny soda straws, are about 3 to 5 mm long; the diameter is 1/100 of their length. The center of the cell is hollow. Water that is in the hollow space is called free water. It could be removed by blowing it out of the cell. (Actually, we call the liquid "water," but the water contains many other chemicals--just ask anyone who likes maple syrup on their pancakes what the water in wood tastes like!) The cell wall itself (which is actually 1.5 times heavier than water, so wood actually doesn't float--the air in the hollow spaces makes wood float) also can absorb water. The wall can absorb up to 30% of its weight in water. This absorbed water is called bound water, as it is held in the cell wall by hydrogen bonding.

When drying wood, the free water leaves first. It requires less energy to evaporate than the bound water. At about 30% MC, all the free water is gone and just bound water remains. At 99.9% RH, the MC of the wood will stay at about 30%. But, if the RH is lower, the bound water will evaporate--for example, 80% RH is 16% MC, 50% RH is 9% MC, and 30% RH is 6% MC.

Setting the Pitch

In addition to water in the hollow spaces of the cells in softwoods, there is a material we often called sap, resin, or pitch. This sticky material has many properties, but one problem is that the pitch tends to ooze out of the wood for years. So, what we like to do with resinous softwoods is to heat the wood for a day or two to evaporate the pitch (or at least evaporate the pitch that will be liquid at room temperature). We typically go to 160 F. What does this do to musical properties? I don't know, but it is the only way to get the pitch problem solved. (Incidentally, if you heat a wood like cedar, it drives off the pitch, but then the wood smells rather bland, rather than the nice gerbil smell that we expect from cedar. Probably any moth killing properties are lost too.)

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

Click on Wood Doctor Archives to peruse past answers.

If you would like to obtain a copy of "The Wood Doctor's Rx", visit the Wood Education and Resource Center Web site for more information.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Lumber & Plywood: Storage

  • KnowledgeBase: Primary Processing: Air Drying Lumber

  • KnowledgeBase: Primary Processing: Kiln Operation

  • KnowledgeBase: Primary Processing: Lumber Grading

  • KnowledgeBase: Wood Engineering: Wood Properties

  • KnowledgeBase: Knowledge Base

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2021 - Woodweb.com
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review Woodweb.com's Copyright Policy.

    The editors, writers, and staff at Woodweb.com try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at Woodweb.com after considerate evaluation, and at their own risk.

    865 Troxel Road
    Lansdale, PA 19446

    Contact Us

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article