Effect of Painting Treatment on Visible Light Reflection Considering Cellular Structure Inside Wood

In order to clarify the mechanism of change in reflectance of visible light due to painting treatment, X-ray CT observations of the internal structure of the material and measurements of the optical properties of visible light with a spectrophotometer were performed for two types of grain of hinoki cypress (Chamaecyparis obtusa) with various amounts of paint. In the observation of CT images, penetration of the paint into the material was not confirmed in the edge-grain samples, whereas that was confirmed in the end-grain samples. In addition, the permeability of the paint of the end-grain samples was quantified, and that was in a positive relationship with the paint amount. In the optical characteristics measurements, in the medium to long wavelength range, there was no increase in absorption but a decrease in reflectance due to an increase of transmittance. There was also a decrease in reflectance due to an increase in the amount of penetration. From the above results, it was shown that the mechanism of lightness reduction by the clear painting treatment is affected by an increase in the value of the transmittance in the medium to long wavelength regions due to differences in the amount of paint penetration.