Near-Infrared Transmitted Light Observation of Wood Anatomy: Comparison of Hardwoods and Softwoods Under Air-Dried and Water-Saturated Conditions

A near-infrared (NIR) light transmission imaging system was constructed using a stereomicroscope equipped with an 860 nm NIR LED light source to evaluate its applicability for observing wood anatomical structures. Species identification of wooden Buddhist statues is important for clarifying their provenance and production period, but such objects require non-destructive examination, and surface darkening from aging and soot deposits often limits observation under visible light. Fifteen wood species used for Buddhist statues and other cultural and architectural properties—eight hardwoods and seven softwoods—were examined, and NIR transmission images of the transverse section were obtained under air-dried and water-saturated conditions. Under air-dried conditions, NIR transmittance differed among species and between heartwood and sapwood, revealing anatomical structures such as vessels, growth-ring boundaries, and resin canals. Under water-saturated conditions, transmittance increased in all species and resin-canal structures became more distinct in softwoods, although some image blurring occurred. These results indicate that NIR transmission observation is effective for non-destructive species identification of wooden cultural properties, and that wood moisture strongly affects the resulting transmitted image.