Abstract
Interesting aesthetic properties of tropical woods, like surface texture and colour, are rarely impaired due to weathering, rotting and other degradation processes. This study analyses the colour of 21 tropical woods before and after six weeks of intentional attack by the brown-rot fungus Coniophora puteana. The CIEL*a*b* colour system was applied for measuring the lightness, redness and yellowness, and from these parameters the hue tone angle and colour saturation were calculated. Lighter tropical woods tended to appear a less red and a more yellow, and had a greater hue tone angle. However, for the original woods was not found dependence between the lightness and colour saturation. Tropical woods at attack by C. puteana lost a weight from 0.08% to 6.48%. The lightest and moderately light species—like okoumé, iroko, ovengol and sapelli—significantly darkened, while the darkest species—wengé and ipé—significantly lightened. The majority of tropical woods obtained a brighter shade of yellow, typically wengé, okoumé and blue gum, while some of them also a brighter shade of green, typically sapelli, padouk and macaranduba. C. puteana specifically affected the hue tone angle and colour saturation of tested tropical woods, but without an apparent changing the tendency of these colour parameters to lightness. The total colour difference of tested tropical woods significantly increased in connection with changes of their lightness (ΔE*ab = 5.92 − 0.50·ΔL*; R2 = 0.37), but it was not influenced by the red and yellow tint changes, and weight losses.
Highlights
The surface appearance of wood is often evaluated by examining its texture, roughness, and colour [1,2,3]
The aim of this study was to determine the colour changes of 21 tropical woods when exposed to the brown-rot fungus C. puteana, which can cause an important deterioration of wood products in the interiors of buildings
Several tropical woods have positive surface characteristics, such as interesting texture and colour, and high natural durability, which is an essential requisite for wooden constructions exposed to the environment with a high risk of biodeterioration by fungi and insects
Summary
The surface appearance of wood is often evaluated by examining its texture, roughness, and colour [1,2,3]. The colour of an individual wood species is predetermined by the type and amount of extractives, by the surface roughness and moisture, and by the direction of light irradiation [4]. The CIE 1976 L* a* b* colour system classifies the temperate and tropical wood species into the positive octant with the lightness (L* ) from 20 to 90, the redness index (+ a* ) from 0 to 20, and the yellowness index (+ b* ) from 10 to 30 [1,5]. The tropical wood species occupy a much greater portion of the colour space in comparison with temperate (for example European) species [7,8]. Within a defined wood species, the colour variations can be influenced by more factors, mainly by its chemical and anatomical structure [9] and specific genetic parameters [10], and by environmental conditions at growth [11,12], atmospheric effects at exposure in exteriors or interiors [13,14], and biodeterioration processes [15,16,17]
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