Color variations in CIELAB coordinates for softwoods and hardwoods under the influence of artificial and natural weathering

Abstract

Artificial and natural weathering treatments have been shown to influence the chemical and physical properties of wood and wood-based materials, e.g. moisture content, density, composition and coloration. Changes in color caused by natural and artificial sources of ultraviolet radiation (UV) are an important topic to be studied in wood, and have been addressed in this work for eight strength classes of timber species (hardwoods and softwoods). Color measurements were carried out according to ABNT NBR 7190:1997 normative document by the CIE-L*a*b* (CIELAB) system, with L* representing lightness, and a* and b*, red/green and yellow/blue coordinates, respectively. For the samples studied herein, a* and b* approached zero after exposure to artificial UV radiation, when a gray tonality was noticed in dark-colored surfaces. Naturally weathered samples, on the other hand, responded more effectively to long-term UV exposure (360 days) for all color-space parameters, both hardwoods and softwoods. This implies that effects of air pollution and other degradation-aging factors need to be considered. Results of statistical analysis also contributed to quantify changes in color after artificial and natural weathering treatments.