The purpose of our study was to clarify the influence on wood color of relative humidity (RH) in conditioning, or process of evaporating water, of dye-aqueous solution impregnated wood. The cross-cut (RT) or quarter-sawn (LR) sample of hinoki (Chamaecyparis obtusa) was impregnated with a 0.1 mass% aqueous solution of patent blue VF (PB), and subsequently conditioned at several levels of RHs (40 °C) to reach to a constant mass. The conditioned samples were dried at 40 °C over phosphorus pentoxide in a vacuum and observed by microscope, and each parameters of the sample in L*a*b* color space were measured by color spectrometer. With the increase in RH, the values of L* and b* for the RT and LT surfaces of the RT and LT samples, respectively, increased and became closer to those for the untreated samples. This was considered to be caused by the decrease in the amount of PB on the surface of cell walls with increasing RH because of the increase in the diffusivity of PB into cell walls. In the RT cross section of LR sample, the area of the deeper color was concentrated into the center of the cross-section if the RH was high, which indicates the macroscopic diffusion of PB from the surface to the center in the sample.
