﻿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 strolus 

 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 is 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 European oak (Quercus rohur 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- 

 struction 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 (T axodium distichum (Linn.) Rich.) that the 

 darker the heartwood the more durable it is, but in realhVy 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 



