Color Changes of Various Wood Species in Response to Moisture

Abstract

Color including texture and gloss is one of the most important esthetical attributes of wood. For any porous materials in contact with water, the phenomenon of surface darkening arises from a change in the refractive index, as water enters air-filled pores. For the first time, this research investigated to what extent MC differences affect the surface color, below fiber saturation and after the pores are filled with water, with respect to extractive contents. Samples from 13 wood species were exposed to various climates, and as soon as EMC was reached, the color was determined. Color changes were also recorded after water submersion and also after vacuum impregnation in water. Chromaticity parameters a* and b* widely increased, along with higher moisture contents. Lightness changes were mostly stable at lower moisture contents. An exception was demonstrated by the heartwood species black locust, plum, walnut, and oak, which showed a brightening effect at lower moisture contents, followed by the darkening phase. The overall darkening of wood at high RH is connected to capillary condensation. Liquid water present in the cell lumen most caused darkening and an intensification of hue (increase in a* and b*). Darkening was even more expressed after vacuum impregnation with water. In conclusion, with only limited fluctuations in moisture contents below fiber saturation, the expected color changes are minor to neglectable.

Development and Evaluation of the Chromatic Behavior of an Intelligent Packaging Material Based on Cellulose Acetate Incorporated with Polydiacetylene for an Efficient Packaging

“…Values of ∆E* higher than 3.5 can be visible to the naked eye, as previously achieved in this study at the condition of long UV irradiation time and high temperature, indicating that this intelligent packaging can be used successfully as a sensor of temperature conditions [34][35][36]. The color transitioning from blue to red can be observed in Figures 4 and 5, even though pH and temperature values were not significant at 5% for the adjusted statistical models.…”

Colour changes and equilibrium moisture content on thermomechanical densified wood

“…Parameter a* showed a strong and negative association with equilibrium moisture content, in other words, a reduction in this property caused the opposite effect on the a* coordinate. These results indicate that color change presupposes a change in the equilibrium moisture content, corroborating the literature (Budakçi et al 2012, Baar et al 2019.…”

A Comparative Analysis of Tannin and Commercial Fire Retardants in Wood Fire Protection

“…As observed in the present study, it is expected that tannin reddens the wood [45], due to the presence of molecules with chromophore bonds which are responsible for light absorption, a characteristic common in phenolic compounds [46]. Specifically, tannins stabilize in red-orange colors, contributing to the observed reddening effect [47].…”