DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. 15 
of color. Light is necessary. Ordinarily these color changes are 
deepened by direct sunlight, which has a greater influence on the 
color changes than diffused light. 
Green wood usually differs in color somewhat from air-dry mate- 
rial of the same species, even on a freshly cut surface. There is a 
tendency for the more delicate tints to be obscured by drying. A 
system of color standards is at present sadly needed in describing 
colors of wood (53). Furthermore, the condition of the wood, that 
is, Whether green, partly air dry, or fully air dry, invariably should 
be given consideration. 
The heartwood of sugar-pine, eastern white-pine (Pinus strobus 
Linn.), and western white-pine lumber often becomes a pink, light- 
red, or vinous-red color upon air drying. This color is not confined 
to the surface layer, but is usually uniform throughout. No reduc- 
tion in strength results. Wood of this kind is very pleasing to the 
eye, so it is often desired by pattern makers. This discoloration 
need not be confused with an incipient decay, since it 1s so uniform 
throughout. Furthermore, it terminates abruptly in a horizontal 
direction and does not shade off gradually into the normal light- 
brown or cream-colored wood. 
Color is considered an index of strength properties (14, p. 359-360) 
in certain cases. The French marine department distinguishes two 
classes of Kuropean oak (Quercus robur L.), inferior wood (bois 
maigre) and good wood (bois gras). The former, which is straw 
yellow in color on a fresh cut, is much more subject to atmospheric 
influences; that is, it shrinks, swells, warps, twists, and splits more 
readily than the latter, which is pale brown to red brown in color. 
This is taken into account in specifying in what part of the con- 
stcuction the two types of wood shall be used. The Danish-Prussian 
marine specifications distinguish three colors of green oak wood, 
whitish yellow, brownish yellow, and reddish yellow, all three fre- 
quently with a tinge of gray. The first color on drying becomes 
straw-colored or sand gray, the second greenish brown, and the third 
reddish yellow or a dirty or dusty yellow-brown. It is considered 
that the unseasoned or fresh wood with any brownish color is de- 
cidedly poor in quality. 
The foregoing seems to be somewhat contradictory. In the opin- 
ion of the writer, trusting to the vagaries of color is an exceedingly 
uncertain method by which to judge the strength properties of wood 
within a species or group and has nothing to recommend it as com- 
pared to the reliable index of the ratio of summer wood to spring 
wood per annual ring, which is particularly easy to judge in ring- 
porous woods like oak. There is a widespread opinion in regard to 
southern bald cypress (Taxodiwm distichum (Linn.) Rich.) that the 
darker the heartwood the more durable it is, but in reality the color 
of the heartwood makes no difference. 
Most woods when dried after a prolonged immersion in water 
reveal a grayish, lusterless color, much like that caused by steaming 
(see p. 10). Oak changes to a blue-black or a gray-black color 
after such treatment. 
Wood becomes a dirty gray to gray-black color after long exposure 
to the elements. This is well illustrated by unpainted poles, fence 
rails, posts, and shingles. The color change is caused by a number 
