Wood Aging. Characteristics of aged Hinoki wood from Japanese historical buildings
M Yokohama, S Kawai
Wood has always played a major role in Japanese traditional culture. More than 90% of buildings listed as a National property or a nationally important cultural property of Japan are constructed with wood. In the ancient capitals Kyoto and Nara, many traditional wooden buildings were inscribed as World Cultural Heritage of the UNESCO. The most famous and the world’s oldest wooden construction still standing is Horyu-ji temple from the latter half of the seventh century.
Wood is present in many cultural heritage objects thanks to its capacity to resist over long period of time. However, the evolution of its properties in regular use remains insufficiently known. The present study on the effect of wood aging takes advantage of the Japanese context where building traditions have been maintained for centuries.
One major difficulty for the research on “aging of wood” is the gathering of suitable samples, with well-defined origin, certified dating and permission of publication by conservation administration. The Japanese context, where traditional uses of wood have been maintained for more than 1600 years, offers a unique opportunity to address the question of wood aging. Since 2004, the wood samples from various temples and other historical buildings were being gathered by the Research institute for Sustainable Humanosphere, Kyoto University, Japan.
The matching of specimens from different origins is another typical obstacle. Wood is a variable material due to genetic variations and dependency on growing conditions of the trees. To discuss property changes due to aging, a recent reference is required. However, it is difficult and sometimes impossible to obtain recent wood that closely matches a given old wood sample. To overcome the difficulty, thermally treated wood as an accelerated aging can be used to produce corrections that will allow comparing data from slightly mismatched samples. Thermally treatment ware performed at 90, 120, 150, and 180℃ for various periods on new hinoki wood from Kiso area.
This paper deals with mechanical characteristics of aged hinoki (Chamaecyparis obtuse Endl.) wood from Japanese historical buildings and thermally treated hinoki wood, especially their Young’s modulus, rapture energy and hygroscopisity. It is not only for the basic science study on aging of wood by using unique and indigenous Japanese hinoki wood, but also for the commonality and universality of worldwide wooden cultural assets. This research will have a positive role on preservation and conservation of wooden cultural properties in the world.