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Decorative pattern showing up on wood surface, because of special and abnormal alignment in cell or tissue, is generally called a figured grain. Because the figured grain is characteristically seen by human eye position and by the angle of incident light, it is prized. For this reason, optical characteristics in the figured grain are considered very important. Accordingly in this study the spectral reflectivity in the broad ray area and the axial element area was measured on surface figured with tiger stripes of Japanese oak (Quercus crispula) , and how the spectral reflectivity concerns relatively to surface roughness was studied. The main results are shown as follows :1) When the broad ray area was illuminated perpendicularly to the grain, the reflectance curve showed a clear peak in a condition of the mirror reflection. Meanwhile the reflectance curve was gentle in the axial element. When the both broad ray and axial element areas were illuminated parallel to the grain, the reflectance curve showed almost the same pattern.2) When the surface was illuminated perpendicularly to the grain, the difference of lightness between the axial element and the broad ray area was recognized easily compared with the incidence parallel to the grain. When the surface was illuminated parallel to the grain, the difference of lightness between the axial element and the broad ray area was small and indistinguishable.3) The difference of L*, a*, b* between both the axial element and the broad ray area was bigger in the incidence perpendicular to the grain than the incidence parallel to the grain.4) The surface roughness parameter of the axial element showed more than that of broad ray area. It is regarded that the surface roughness has an effect on optical characteristics corresponding to each incident direction. As a result, the surface of the broad ray area in Japanese oak appears in silver or black color, depending on the incident and receiving angle of light, contrasted with axial element areas.

Visual Characteristics of Japanese Oak (Quercus Crispula) Surface Figured with Tiger Stripes