Discoloration of heat-treated and untreated red alder wood in outdoor, transitional and indoor space

Wood heat treatment has been held an effect way to adjust wood color. To obtain a better understanding of the in-service color stability of heat-treated wood, heat-treated and untreated red alder boards were exposed to outdoor space, indoor space lit by LED lights and transitional space of a bay window for one year. The evolution of CIELAB color parameters was recorded and the chemical changes of the irradiated boards were analyzed using Fourier transform infrared spectroscopy. It was found that the heat treatment significantly darkened the wood, and higher treatment temperature led to a darker appearance. The exposure tests lowered the color difference caused by the treatment. The color stability of heat-treated and untreated wood is space and time dependent. The indoor space exerted limited influence on wood color. The outdoor space eventually turned the board color to silver gray with the combined forces of photodegradation and leaching, which basically eliminated the visual difference between different types of boards. In the transitional space, all the boards experienced a yellowing process mainly induced by longer wavelength light, to which, the heat-treated boards were more sensitive and showed greater color change than the untreated ones.