Quality control of thermally modified timber: Interrelationship between heat treatment intensities and CIE L*a*b* color data on homogenized wood samples

There is increasing awareness of the durability, dimensional stability, and strength properties of thermally modified timber products. Appropriate standards and test methods for industrial-scale quality control are needed. The aim of this study was to investigate the suitability of CIE L*a*b* color measurements for implementation in industrial quality control. Good linear correlation was found between a cumulated measure of L* and b* data and the heat treatment intensity for spruce (Picea abies Karst.), pine (Pinus sylvestris L.), and beech (Fagus sylvatica L.). Wood samples homogenized by milling revealed less variation in color values compared to wood surface measurements. Thus, measurements on milled wood are recommendable to obtain results with high statistical significance. Color measurements are rapid, precise, and highly reproducible. Based on the strong correlation between color data and heat-treatment intensities, color measurements could easily be implemented for quality control of thermally modified timber.