Proceedings e report - Firenze University Press

AGING WOOD FROM CULTURAL PROPERTIES COMPARED WITH ACCELERATED AGING - COLOR PROPERTIES
Δ L*
= Lt
* -Lr
*
(1)
2
2
2 1/
2
Δ E = [( ΔL*)
+ ( Δa*)
+ ( Δb*)
]
(2)
where Lt* is the lightness of the treated specimen, Lr* is the average of 83 untreated specimens as a
reference, and Δa* and Δb* are the chroma differences based on the untreated specimens. Nine to
sixteen and three to five specimens were tested at each condition for naturally aging wood and
accelerated aged wood, respectively. Three locations in each specimen were measured, and the
average values with standard deviations were calculated.
Table 1: Naturally aging wood samples.
Sample Temple Aging time [year]
A Horyuji, Gojunoto 1618.5
B Horyuji 1467.5
C Horyuji, Gojunoto 1548.0
D Horyuji 1530.5
E Horyuji 1319.5
F Horyuji 899.0
G Horyuji 822.5
H Senjuji, Mieido 732.5
Table 2: Accelerated aged wood samples.
Treatment temperature [ o C] 90 120 150 180
Treatment time [hour] 256~12288* 32~7680 4~960 0.5~120
*The treatment at 90oC is now in processing and planed up to 61440 hours (approximately 7 years).
3. Results and discussion
3.1. Color Changes
Fig. 1 shows the specimens of naturally aging and accelerated aged wood. The color of naturally aging
wood and accelerated aged wood were darkened with aging and treatment times, respectively. Fig. 2
shows the changes of the lightness (L*) and the color difference (ΔE) of naturally aging wood and
accelerated aged wood. In naturally aging wood, L* decreased and ΔE increased with aging time. In
the case of accelerated aged wood, L* decreased and ΔE increased with treatment time over all of the
treatment temperatures. These behaviors can be described as sigmoidal curves. Similar trends
irrespective of treatment temperatures implied that the color changes were caused by the same
mechanism.
a b
Naturally aging
58
a c
Accerelated aged
Fig. 1: Color change of natural aging and accelerated aged wood
a: control (untreated wood), b: aging for 1400 years, c: heat-treated at 120°C for 320 days.