. Defects in timber caused by insects. Wood; Forest insects. 40 BULLETIN 1490. U. S. DEPARTMENT OF AGRICULTURE In oak the black checks are larger, often 6 inches long over an area of several square inches. In quarter-sawn boards they appear as dark distorted or curly wood and run through many layers of wood, while in bastard-sawn boards they form black scars several inches long by 1 or 2 wide. In the Ozark Mountains of Arkansas this is a very common defect. Timber from softwoods or hardwoods is not seriously reduced in strength by such defects, but the wood is lowered in grade and rendered use
. Defects in timber caused by insects. Wood; Forest insects. 40 BULLETIN 1490. U. S. DEPARTMENT OF AGRICULTURE In oak the black checks are larger, often 6 inches long over an area of several square inches. In quarter-sawn boards they appear as dark distorted or curly wood and run through many layers of wood, while in bastard-sawn boards they form black scars several inches long by 1 or 2 wide. In the Ozark Mountains of Arkansas this is a very common defect. Timber from softwoods or hardwoods is not seriously reduced in strength by such defects, but the wood is lowered in grade and rendered useless for finishing, turning, staves, and woodenware. It can, however, be used for structural material or for purposes for which the marred appearance will not be detrimental. Since black check is always the result of injury to the living tree, it is not preventable, from the lumberman's standpoint. DEFECTS CLASSED AS BLUING OR STAINING Bluish-black streaks or stains in the sap wood of pine, especially in southern yellow, western yel- low, and sugar pines, as well as in certain hardwoods, such as red gum or sap gum, are classed as bluing. This defect occurs either in the standing tree or in recently cut green logs or green lumber and is caused by fungi de- veloping from spores which are no doubt carried by insects. In pines the bluing directly follows in- festation by tree-killing bark beetles41 in the standing trees (fig. 44) {29). This defect can be prevented only by the control of tree-killing bark beetles. Similar staining defects are caused by many ambrosia beetles42 in both the living trees and green saw logs and green, freshly sawn lumber. (Figs. 4, 9, and 13.) This staining can be prevented in green saw logs by prompt utilization of the green logs; by placing them in the mill pond soon after cutting; or by sun-curing. When the lumber is sawn it should be either kiln-dried or air-seasoned rapidly. Bluing is not always dependent on bark beetles (1$).. Fig. 43.—Black chec
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Keywords: ., bookcentury1900, bookdecade1920, bookpublisherwa, booksubjectwood
