Discolouration of white coatings applied on kiln- and air-dried scots pine lumber

During drying, the low-molecular weight (LMW) sugars and nitrogenous compounds are redistributed and accumulated at the lumber surface. These soluble substances may migrate into coatings and cause discolouration. The aim of the present study was to determine the susceptibility to discolouration of white coatings, applied on kiln- and air-dried lumber surfaces with different content of LMW sugars and nitrogen.The differences in the discolouration were more distinct between the coatings than between the drying treatments. Planing had no significant effect on the discolouration, which proved that the different content of soluble substances at the original and planed surfaces did not induce significantly different discolouration. The type of drying and the actual contents of soluble substances at the surface, played a minor role in the discolouration process. The discolouration of all five coatings can be characterized as “fading”, due to decreased colour saturation and lightness.