When the outside temperatures fall below inside temperatures, as in Winter, the cold, moist air entering the heated building becomes hot, dry air. In the same way that moisture in the air will be absorbed by materials in a building, this hot, dry air pulls moisture from everything it comes in contact with, trying to reach "equilibrium" (the point at which the material no longer loses or gains moisture).

If you take wood from outdoors that has equalized with the outside air moisture content, into a heated building with a lower moisture content, the wood will begin to give up its moisture to the dry air in the building. As the wood loses moisture it will shrink and begin to crack and check. If the wood doesn't crack, then warping is the result. But damage to the wood is just the beginning of dry air problems in a woodworking environment.

Dry wood will suck the solvent from glues before they can properly cure, leaving only the glue residue to form a very weak joint. Shrinkage of the wood in the glue joint can then literally pull it apart. Dry wood also sucks solvents from paints and finishes, often leaving a rather dull finish that won't last very long.

Cutting and sanding dry wood results in a much higher production of dust due to the dry wood fibers breaking off during the process. Moist wood fibers cut more easily, rather than breaking, and will also reduce the sharpening frequency required with many blades.

In musical instruments, wood that is too dry can affect the quality of the sound it produces. Guitars, whether electric, acoustic or Spanish, need to be built in humidity controlled environments to insure the rich sound musicians expect. Of course, proper storage of a Stradivarius violin in a humidity controlled environment is a foregone conclusion.

Mahogany sounding boards used in pianos require proper humidity control or they will dry out and produce poor quality sound. In addition, as the pegboards dry out the pegs become loose and the piano will require more frequent tuning.

In the case of a museum, where expensive paintings, sculptures and other hygroscopic materials are kept, rapid changes in Relative Humidity can be devastating and will eventually destroy the wooden artifacts in short order.

The key to protection of wood and wooden articles is stability of the environment. It is detrimental to permit the Relative Humidity to vary rapidly or widely throughout the year.

In most woodworking environments, a Carel humidification system will pay for itself in reduction of scrap and quality improvement in less than 1 year. Woodworkers should also recommend to their distributors that their high quality furniture, instruments and cabinets be stored and displayed in a humidity controlled environment, and that the final customer do the same.

Want to learn more about furniture and humidity? http://aic.stanford.edu/library/online/brochures/furn.html