Because of controlled drying rates and conditions kiln-dried wood is often superior to air-dried wood.
Air drying is more likely to yield bacterial decay, insect damage, warped, and checked staves. Most competent wood bowmakers have evolved stave curing systems which work for their local woods and climate. But if you ever find yourself in the company of wood bowmakers, don't bring up the subject of purchased staves. Unless you want to hear grown men moan, swear, and tell competing horror stories. If tree-split staves are not very carefully seasoned they will be inferior to kiln-dried counterparts.
Kiln drying is more likely to cause internal cell collapse: High temperatures partially plasticize cellulose in wood cells. In extreme cases a surface which dries too fast will compress its wetter, weaker core, collapsing these plasticized cells. But unlike earlier times, the causes of such collapse are well understood now, and easily avoided.
Too-rapid air drying can collapse core cells also, especially with larger diameter stock. Direct sun, low humidity, and brisk winds cause surface wood to dry and shrink much faster than core-wood.
When done properly, both drying methods yield equally straight and strong bows.
When done improperly, both methods leave tell-tale clues: Sunken or rippled surfaces point to cell collapse. Avoid checked and warped wood, regardless of how it was dried.
Maybe one board in 25 shows some sign of drying damage, usually only mild
Arriving at the lumberyard at about 8.5% moisture content, two weeks of basement seasoning rehydrated this board. Now at 10% and ideal for my near-the-bay microclimate. Five miles east, just over the Berkeley Hills, 8.5% would be ideal.
Checking. Inspecting for these signs of damage pays off. After making hundreds of bows from kiln-dried staves, I can't report a single example of failure due to kiln-damage.
One misconception concerning kiln-dried wood is that it is too dry. Forcedrying wood with artificial heat is expensive. Taking moisture content lower than equilibrium is bad business. Hardwoods generally leave the kiln at about 8%, just right for moderately dry areas of the continent. Wood headed for moister areas often leaves the kiln at an appropriately higher moisture content — hardwoods shipped to Louisiana often being damper than if shipped to Arizona.
A lumberyard stave is more likely to be close to local equilibrium than a local air-dried stave. Unless reduced to near-tillered dimensions, wood takes a very long time to reach local equilibrium.
As with any stave acquired from outside your area, allow time for de - or re-hydration to local equilibrium. Once reduced to slightly-bending blanks, only a few days are usually needed. Here too, a moisture meter or a balance beam is helpful — balance the stave on one end of a fairly long, light rod, an equal weight on the other. Suspend the rod at its point of balance by a string. As the stave gains or loses moisture, it will rise or fall. Adjust the string to keep the rod parallel to the ground. When no change in balance has occurred for a few days, the stave has reached equilibrium.
Wood Strength, or stiffness, rises about 6% per 1% change in moisture content. This means same draw-weight bows made of wetter wood will have more mass. Drier wood will have less mass, but be more brittle. 8% to 11% is a good range. Between 9% and 10% is ideal.
Another misconception is that kiln-drying damages wood due to overheating. This after centuries of successful steambending at 212-degrees. Kilns generally operate at about 170 degrees.
Steam bending weakens wood by up to 25%, depending on the severity of the bend. But safe bows nevertheless result because tillering compensates: weaker portions are automatically left thicker. The same tiller-induced strengthening should occur in staves with mild cell collapse; again, weaker areas are left thicker, and are therefore stronger.
World History
