Gray-Brown Chemical Stain in Southern Hardwoods.

摘要

From time to time southern hardwood lumber manufacturers encounter a troublesome and costly staining problem-- troublesome because this stain develops in chemically dipped as well as undipped sapwood lumber, and costly because, unlike blue stain, it may show up only after final lumber surfacing in the plant. This nonfungus, gray to brown chemical stain develops rapidly under favorable temperatures and poor drying conditions, especially in the South, where prolonged wet seasons are common. It frequently occurs in soft maple, hackberry, hickory, red oak, and dogwood, where it takes on the appearance of a blue stain. Unfortunately, the chemical stain is not as readily visible as blue stain on rough surfaces; chemical stain usually does not appear until the wood has been planed. This happens because the surface fibers of wood usually dry rapidly enough even under poor drying conditions to prevent stain development. The wood immediately beneath, however, remains wet long enough to allow the chemical stain to develop. The stain is thought to be the result of oxidation and enzymatic action on certain materials stored in wood cells and it develops when favorable conditions of moisture and temperature exist. In the spring of 1958, slides were made from thin sections of stained hickory and red oak and examined under the microscope. The stain appeared to the naked eye as a brown general discoloration over the wood surface. Under the microscope, however, the stain was found to be present only in ray parenchyma cells of the wood. These cells serve for food conduction and storage and are rich in carbohydrates and possibly other materials. Because of the closeness of wood rays to each other, the stain coloring appeared to cover the general area.