Proceedings e report - Firenze University Press

EVALUATION OF THE AGING WOOD FROM CULTURAL PROPERTIES AS
COMPARED WITH THE ACCELERATED AGING TREATMENT
-ANALYSIS ON COLOR PROPERTIES-
Miyuki Matsuo 1 *, Misao Yokoyama 1 , Kenji Umemura 1 , Junji Sugiyama 1 , Shuichi Kawai 1 , Shigeru
Kubodera 2 , Takumi Mitsutani 2 , Hiromasa Ozaki 3 , Minoru Sakamoto 3 , Mineo Imamura 3
1 Research Institute for Sustainable Humanosphere, Kyoto University, Japan
2 Nara National Research Institute for Cultural Properties, Nara, Japan
3 National Museum of Japanese History, Japan
Abstract
In this paper, we studied on the color change of wood during aging comparing the naturally aging wood with the
accelerated aged wood. Naturally aging samples of Hinoki (Chamaecyparis obtusa Endl.) were collected from
historical properties. For accelerated aged samples, recently felled down Hinoki specimens were heated in the air
at the temperature of 90, 120, 150, and 180 o C. Applying kinetic analysis to the measured color data, it was
concluded that the color change during natural aging was mainly explained as a mild thermal oxidation process
at the ambient temperatures.
1. Introduction
In Japan, there are many wooden cultural properties and historical buildings such as Horyuji temple
which is the oldest wooden building in the world. The elucidation of aging mechanism of wood is
important not only for the preservation and restoration of wooden cultural properties but for the basic
research of wood. This is the significant mission of Japan that provides long history of wooden
culture.
Though some empirical data suggest that the aging of wood is a mild thermal oxidation at the room
temperature [1-3], few papers have reported on the theoretical evaluation and the detail mechanism.
On the other hand, sculptors and carpenters have used the color of wood as a criterion of aging. This
may be because the color properties directly express chemical change of wood. In this study, color
properties were used to evaluate the aging mechanism of wood; color properties of naturally aging
wood samples cut out from cultural properties and aged wood samples accelerated by heat treatment
were measured and compared. Kinetic analysis was performed based on the relationship between time
and temperature.
2. Materials and methods
Hinoki (Chamaecyparis obtusa Endl.) which is the typical members for traditional buildings and
Buddhist sculptures in Japan was chosen as wood species. Eight naturally aging wood samples
collected from historical buildings [4] were used as shown in Table 1. The year of wood formation
was determined by dendrochronology and radiocarbon dating. The detected years agreed with the old
documents. Aging heartwood specimens, being free from bio-degradation and weathering, were cut
out with the dimensions of 60mm (L) x 10mm (R) x 2mm (T). For an accelerated aging specimen,
360-year-old air-dried Hinoki from Kiso, Japan was used. Specimens were cut out with the dimensions
of 120mm (L) x 20mm (R) x 4mm (T) from the outermost part of the heartwood. The samples were
dried at 60 o C and then heated by the oven at the temperatures ranging from 90 to 180 o C. Table 2
shows the maximum treatment time of the specimens at each treatment temperature.
The color of the specimens was measured with a spectrophotometer (KONICA MINOLTA CM-
2600d) under a D65 light source and observer angle of 10 degrees. The sensor head of the
spectrophotometer was 8 mm in diameter. The CIELAB color parameters (L*, a*, b*) were used to
express the color change. The differences in the lightness (ΔL*) and color (ΔE) were calculated using
the following formulas:
* E-mail: matsuomiyuki@rish.kyoto-u.ac.jp
Joseph Gril (edited by), Wood Science for Conservation of Cultural Heritage –Braga 2008: Proceedings of the International
Conference held by COST Action IE0601 (Braga - Portugal, 5-7 November 2008, ISBN 978-88-6453-157-1 (print)
ISBN 978-88-6453-165-6 (online) © 2010 Firenze University Press