WoodSense: Spotlight on Walnut

A wood that’s a pleasure to work, and a joy to behold

Black walnut (Juglans nigra), which tops many lists of favorite furniture woods, also has a surprisingly multi-faceted role as a nation-builder. As early generations of American furnituremakers were discovering the splendor of this dark domestic wood, pioneers and colonists were harvesting the tree’s nuts for food and employing the easy-splitting, decay resistant walnut logs for split-rail fences and log–and timber–framed homes. Because of the wood’s balanced attributes of strength, stability, and shock resistance, the U.S. military from the Revolution up to the end of the 20th Century relied on black walnut for gunstocks.

Walnut trees may not play as important a role in our daily lives today, but the lumber continues to be a workshop favorite.

Where the wood comes from

Walnut trees can be found across the U.S. and in areas of southernmost Canada, but most of the commercial wood comes from the Central U.S. You’ll find the finest trees in Iowa, Minnesota, and Wisconsin along the Mississippi River Valley.

Claro walnut is one of black walnut’s closest and prettiest cousins. Typically identified as Juglans hindsi, there’s some confusion as to the exact species. Hailing from California and Southern Oregon, it’s sometimes referred to as California walnut. It exhibits a pronounced color and figure, particularly near the base of a trunk that had European walnut grafted to it for increased nut production. Old orchard trees often reveal great beauty within when harvested.

Butternut (Juglans cinera) is on the other side of the color and price spectrum. Sometimes referred to as “white” or “poor man’s” walnut, this species is lighter and less expensive than its darker cousins, but it can be stained to match them, making it useful as a secondary wood. Butternut contains fewer extractives and works as easily as pine. While its softness is advantageous for carving, this makes the wood less suitable for furniture parts that need to withstand wear and tear, such as legs and tabletops.

Canker-tastrophe

Black walnut is under attack by the Thousand Cankers Disease (TCD), a fungal malady carried by the walnut twig beetle that lives under the tree’s bark. The fungus creates black cankers that restrict the flow of nutrients and kill affected trees within three years. Unfortunately, other than premature leaf yellowing, TCD doesn’t reveal itself on the trunk until it’s too late.

TCD is rampant in the western states, but cases have also been confirmed in Tennessee, Virginia, and Pennsylvania. To control the spread of this blight, experts advise against transporting walnut logs or boards with intact bark. (Many states restrict the sale of air-dried lumber and live-edged boards across state lines.) Kiln-dried stock poses little threat of carrying the fungus-ridden beetle.

For more information about the disease and prevention tips, go to www.thousandcankers.com.

Air-dried Black Walnut with Sapwood

Kiln-dried Black Walnut with Sapwood

Black Walnut Crotch

Claro Walnut

Butternut

How to select the best stock

Although walnut trees initially spring up quickly, they are slow to mature. The light colored sapwood surrounding the brown heartwood represents 10 to 20 years of growth. To control waste, most commercial dealers use steam in the kiln-drying process to encourage the compounds within the heartwood to migrate and darken the cream-colored sapwood. This process evens out the color, but it also robs the heartwood of its richer colors (see photos, at right).

While many woodworkers might be willing to drive some distance to obtain air-dried stock, regulations intended to contain the spread of the Thousand Cankers Disease (see box, above) restrict transportation of air-dried walnut across state lines. So, if you’re hunting for deeper purples and browns and cream-colored sapwood, search out a supplier using a dehumidifier kiln; its lower-temperature process reduces the moisture and arrests the fungus without affecting the color of the wood.

Working walnut in the shop

Walnut’s beauty is more than skin deep. Falling midway between ring-porous woods like oak, and diffuse-porous woods like maple, walnut is considered “semi-ring-porous.” This gradual cellular transition between early and latewood makes the wood less prone to chattering and tearout and friendly to work with both power machinery and hand tools. Thanks to its moderate hardness, walnut is easy to sand, and it can be polished to a high luster.

Despite its many attributes, you must be mindful of walnut’s natural defenses. Mature trees contain the chemical compound juglone and other extracts that can irritate the eyes and skin, so use common sense. Wear a dust mask or respirator, don goggles when machining, and wash exposed skin afterward. (Juglone can wilt or kill plants and harm horses and dogs, so take care when disposing of shavings and sawdust.)

Finishing walnut

To see what walnut will look like under a clear finish, wipe the wood with mineral spirits or alcohol. If you’re working with air-dried stock, your project may not require much help; a few coats of oil or film-based finish should do the trick. To add extra warmth to kiln-dried stock, try pretreating with orange shellac or aniline dye before the topcoat. Walnut’s semi-diffuse pore structure means that it does not need grain fillers.

To conceal sapwood, try blending in the lighter sections with a dye stain. (The color of heartwood doesn’t change over time.) Staining or shellacking the entire piece can provide additional camouflage, and can help even out the tones of contrasting boards.