Home > Research > Research Results > Research Results 2020 > A non-destructive method has been developed to distinguish between softwood and hardwood in historical wooden statues

Update:October 26, 2020

Main content starts here.

A non-destructive method has been developed to distinguish between softwood and hardwood in historical wooden statues

Article title

The separation of softwood and hardwood in historical wooden statues of the Nazenji-temple in Japan using NIR spectroscopy

Author (affiliation)

Hisashi Abe (a), Yohei Kurata (b), Ken Watanabe (a), Atsuko Ishikawa (c), Shuichi Noshiro (d), Tomoyuki Fujii (e), Mitsuharu Iwasa (f), Hiroaki Kaneko (g), Hiroshi Wada (g)

(a) Department of Wood Properties and Processing, FFPRI, Tsukuba, Ibaraki, Japan.

(b) Nihon University, Fujisawa, Kanagawa, Japan.

(c) Department of Wood Improvement, FFPRI, Tsukuba, Ibaraki, Japan.

(d) Meiji University, Chiyoda-ku, Tokyo, Japan.

(e) Research Fellow, FFPRI, Tsukuba, Ibaraki, Japan.

(f) Seijo University, Setagaya-ku, Tokyo, Japan.

(g) Tokyo National Museum, Taito-ku, Tokyo, Japan.

Publication Journal

IAWA Journal, 41(4), Brill, International Association of Wood Anatomists, November 2020 DOI:10.1163/22941932-bja10038( External link )

Content introduction

In Japan, it has been found that wooden structures of great historical value such as those designated as important cultural assets, national treasures, etc., were made using certain species of wood, such as Japanese cypress, Japanese torreya, camphor, zelkova and so on. However, there are still many wooden statues whose wood species are unknown. Furthermore, there are many cases where the wood cannot be determined to be either softwood or hardwood, especially, wooden statues carved during the Kamakura Period (1185-1333) or earlier whose surfaces have changed over the centuries. Therefore, it has long been desired to develop a method for objectively identifying the species of wood, not only to preserve cultural assets, but also to conduct non-invasive surveys on site.

We prepared several standard samples whose origins were already well established, and created a model that could separate types of wood into softwood and hardwood, according to the spectrum patterns of the samples' near infrared (NIR) absorptions. Using this model, we examined the NIR spectrum from the wooden statues of Nazenji Temple in Shizuoka Prefecture, which is estimated to have been carved during the Heian Period (794-1185). As a result, we found that the wood used for the wooden statues could be separated into softwood and hardwood.

The results also suggested that the better preserved the statue was, the more accurately its wood type could be determined. By using NIR spectra to analyze the surfaces of wooden statues, we found that their wood could be separated into hardwood and softwood, even if they had been carved nearly 1000 years ago. Thus, we could make progress in developing non-destructive techniques for identifying wood species of historical wooden statues.


Photo:Measuring the near infrared spectrum of a wood sample
Photo:Measuring the near infrared spectrum of a wood sample.


Figure1:Results of analyses using the model established

Figure1:Results of analyses using the model established from near infrared spectra.


Figure2:a) Statue classified as softwood

Figure2:a) Statue classified as softwood (well preserved condition); b) Statue classified as softwood (more degraded condition); c) Statue classified as hardwood (well preserved condition); d) Statue classified as hardwood (more degraded condition).