Sap-Stains of Wood

Abstract

SCHEFFER and Lindgren1 present a summary of approximately ten years of field and laboratory work on sap-stains of wood. They state that market demands for wood products are becoming more exacting, making stained wood more difficult to dispose of. Losses from degradation are in general decreasing because of improved methods in controlling stain. Chemical, mechanical, and fungus stains are described and discussed as to symptoms, cause, timber species involved, effect on various wood properties, and control, the major emphasis being on blue stains caused by fungi. In the United States blue sap stains are of greater importance in the south than in any other region, although locally and seasonally important also on the west coast and in northern Idaho and contiguous regions. The chief factors influencing the development of fungus blue stains in sapwood lumber and other wood products are temperature, oxygen, and water. No correlation Was found between wood density and susceptibility to stain. Flat-grained lumber was slightly more susceptible to stain than edge-grained, due to the greater number of rays exposed and the larger proportion of sapwood. Wood once seasoned and remoistened was less susceptible than unseasoned wood, but not significantly so. No difference was found in susceptibility to stain between winter-cut and summer-cut timber.