WOOD EXPLORER
by Gene Wengert
wooddoc@uwalumni.com
Black walnut
Of all the North American species, black
walnut (Juglans nigra) is probably the
species that would receive the title of
“elegant.” It has an aura of being expensive, while yet being very serviceable for
furniture, millwork, cabinetry and flooring.
Oftentimes, thicker (8/4 and 10/4 thicknesses), defect-free pieces ( 8 inches and
wider) demand extremely high prices.
Note that the NHLA grading rules for walnut are different than for all other Eastern
hardwoods. The grading system is based
on small clear areas rather than the large
areas commonly used.
Natural decay resistance of this species and its abundance during colonial
times made it ideal for home construction,
for fences, and for cooking and tableware.
The straightness of its grain, even when
moisture changed, and its ability to absorb
It is.
It looks and
smells expensive.
shock made it ideal for gunstocks. That
use still persists.
Hundreds of years of cutting and high
demand has led to decreased supplies
and resultant higher prices.
When buying walnut, if many smaller
clear pieces are needed, such as for
cabinets, it is more economical to buy a
lower-grade, even though there will be
some waste. When processing upper-grade pieces, donate waste to schools
or non-profit workshops. ❮
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Density. Walnut has a density of 37 pounds per cubic foot.
Kiln-dried lumber weighs about 3 pounds per board foot.
This density is in the middle of U.S. hardwood species.
Strength. Walnut is quite strong. The MOR is 14,600 psi
which compares well to maple and other strong species.
The stiffness (MOE) is 1. 7 million psi, which again is quite
stiff. Hardness is 1010 pounds which is substantial.
Processing suggestions and characteristics
Drying. Walnut dries without much defect, but must
be dried slowly, especially thick stock, to avoid interior
cracks, similar to honeycomb in oak. End coating is essential for thicker stock, and is recommended for thinner
material as well. Shrinkage from green to 6 percent MC
for flatsawn lumber is approximately 6 percent.
Gluing and Machining. Walnut is very easy to glue. Nevertheless, all efforts should be made to assure that gluing
defects never occur, meaning that surfaces should be
flat, straight, and freshly prepared.
Machining properties are excellent. When sanded, a
premium surface is easily obtained.
Stability. Once dried, walnut is extremely stable. Walnut’s shrinkage and swelling rate is lower than many
other North American species. Further, due to its inherent straight grain, warping when the moisture changes
is rare.
Color and Grain. The color of walnut heartwood varies
from greenish to dark brown when first cut. As the wood
ages, it initially turns to a chocolate brown color and then
darkens even more.
Walnut sapwood is white, but is not too wide, so does not
appear on too many pieces of lumber when the logs being
sawn are large. Unfortunately, today log size is decreasing
at the sawmill, so sapwood is becoming more prevalent.
To make the wood more uniform in color, often the wood
is steamed for several days before drying to darken the
sapwood and also to eliminate the greenish hue sometimes encountered. If not steamed, the sapwood is usually
custom-stained in finishing to develop uniform color, but
as the wood subsequently changes color over the years, this
stained area can develop undesirable color contrasts.
Walnut grain is typically straight and uniform; annual
growth rings are not obvious. However, grain deviations do
occur that lead to swirls, ribbon stripes, and other patterns.
