DRYING STRESS
Q:We have bought some hickory lumber and the area under
the sticker is actually lighter than
the surrounding wood. What would
cause that?
A:The stickers used for drying were apparently dry and so when they
were placed on the wet lumber, they
rapidly dried the wood that they were
in contact with. Rapid drying assures
light colored, white wood. However,
the wood between the stickers did
not dry as fast and so it developed a
darker color. I suspect that the wood
was put out for air drying and the
weather was warm and humid, which
caused slow drying and darker colors
in most of the exposed wood...darker
than the wood directly under the stickers. This light color under the stickers
is sometimes called “reverse sticker
shadow.”
The process of soaking
wood in denatured
alcohol is well known
and documented.
Q:Have you ever heard of soak- ing green turned bowl blanks
or even lumber in denatured alco-
hol (for 24 hours) to make them air
dry more rapidly?
A:The process of soaking wood in denatured alcohol (or several
other organic solvents) is well known
and documented. What happens is
that the alcohol replaces the water in
the wood cells. Then, when the wood
is taken out of the alcohol, the alcohol,
partly because it does not have the high
surface tension of water, evaporates
very quickly. Further, as alcohol is a
non-swelling liquid (in finishing we call
it non-grain-raising), the wood does
not shrink when the alcohol leaves. As
a result, we do not see the typical, fast-
drying, shrinkage-related defects, such
as checking. The problem is that the al-
cohol is flammable and also creates air
pollution. In a commercial application of
alcohol or solvent drying, it is necessary
to capture the evaporated solvent to
avoid pollution and to avoid high cost of
the solvent if not recycled. The capture
equipment is expensive however. The
bottom line is that the cost is too high
for alcohol drying to be used commer-
cially today. ❮
Gene Wengert, “The Wood Doctor,”
has been training people in efficient
use of wood for 35 years. He is
extension specialist emeritus at the
University of Wisconsin-Madison.
