Dependence of color on the time and temperature of saturated water steam in the process of thermal modification of beech wood

The aim of the paper is to determine the change of color of wood Fagus sylvatica in CIE L^*a^*b^* color space during the process of thermal treatment of woodturning blanks with dimensions of 40 x 90 x 800 mm by saturated water steam at the temperature from interval t = 105 °C to t = 135 °C and during the time of thermal process 3, 6, 9, 12 hours. Wet beech wood loses its brightness due to the hydrolysis of hemicelluloses and extraction of water-soluble substances. The wood takes on the color shades of varying red-brown color intensity by changes in chromatic coordinates, by increasing the values at the red coordinate a^* and by slight changes at the yellow coordinate b^*. The equations describe the chromaticity coordinates of beech wood in the color space CIE L^*a^*b^* according to the temperature of the saturated steam and the time of the thermal modification of the color τ: L^* = 78.744 + 0.2197·t + 0.6974·τ – 0.0019·t² – 0.0254·t·τ + 0.0728·τ²; a^* = 6.7417 – 0.0074·t + 0.6903·τ + 0.0002·t² + 0.003·t·τ – 0.0459· τ²; b^* = 20.429 – 0.0256·t – 0.1175·τ + 0.0003·t² + 0.0038·t·τ – 0.0175·τ².