Rapid seasoning, except after wood has been thoroughly soaked or
steamed, almost invariably results in more or less serious checking.
All hardwoods which check or warp badly during the seasoning should be
reduced to the smallest practicable size before drying to avoid the
injuries involved in this process, and wood once seasoned _should
never again be exposed to the weather_, since all injuries due to
seasoning are thereby aggravated.

Seasoning increases the strength of wood in every respect, and it is
therefore of great importance to protect the wood against moisture.

Changes rendering Drying difficult

An important property rendering drying of wood peculiarly difficult is
the changes which occur in the hygroscopic properties of the surface
of a stick, and the rate at which it will allow moisture to pass
through it. If wood is dried rapidly the surface soon reaches a
condition where the transfusion is greatly hindered and sometimes
appears almost to cease. The nature of this action is not well
understood and it differs greatly in different species. Bald cypress
(_Taxodium distichum_) is an example in which this property is
particularly troublesome. The difficulty can be overcome by regulating
the humidity during the drying operation. It is one of the factors
entering into production of what is called "case-hardening" of wood,
where the surface of the piece becomes hardened in a stretched or
expanded condition, and subsequent shrinkage of the interior causes
"honeycombing," "hollow-horning," or internal checking. The outer
surface of the wood appears to undergo a chemical change in the nature
of hydrolization or oxidization, which alters the rate of absorption
and evaporation in the air.

As the total amount of shrinkage varies with the rate at which the
wood is dried, it follows that the outer surface of a rapidly dried
board shrinks less than the interior. This sets up an internal stress,
which, if the board be afterward resawed into two thinner boards by
slicing it through the middle, causes the two halves to cup with their
convex surfaces outward. This effect may occur even though the
moisture distribution in the board has reached a uniform condition,
and the board is thoroughly dry before it is resawed. It is distinct
from the well-known "case-hardening" effect spoken of above, which is
caused by unequal moisture conditions.

The manner in which the water passes from the interior of a