建造物における銅及び黄銅製金具周辺に見られた木部の白色化に関する研究：水戸弘道館
孔子廟と旧岩崎末廣別邸を対象にResearch about Whitening Phenomenon of Woods Associated with Copper and Brass Components ofArchitectures: in the Cases of Confucian Temple of Kodokan of Mito Domain and Old Iwasaki-ke
Suehiro-bettei Villa

周 怡杉
Zhou Yishan
1. Introduction

DomainWood adjacent to metal can be adversely affected under
1

The Kodokan of Mito Domain was constructed in 1841, as acertain conditions , which are generally observed in the caseschool to provide education on Confucianism, history,of cultural properties and artifacts. A whitening phenomenon

astronomy, mathematics, music, military strategy, arts, etc.,

of woods associated with metal components is commonlyfor warriors and their children. The Confucian Temple is one

observed in Japanese historic architecture. Until now, whichof the vital constituents of the Special Historic Site ofhas not been profoundly studied.

Kodokan2,3. The original structures were constructed in a

In the Confucian Temple of Kodokan of Mito Domain (水戸style that imitated the Confucian Temple of China, and were

弘道館孔子廟, Mito City, Ibaraki Prefecture, reconstructedruined in 1945 by war. Afterwards, reconstruction wasin 1970s) and Old Iwasaki-ke Suehiro-bettei Villa (旧岩崎家

conducted on the surviving foundation in 1970. The main

末廣別邸, Tomisato City, Chiba Prefecture, constructed instructures were made from zelkova wood (ケヤキ). After the1920s-1930s), the whitening phenomenon of wood adjacent

311 East Japan Earthquake, in order to repair the damaged

to copper and brass components were observed.

parts and enhance structural stability, a restoration wasTo enhance the understanding about this phenomenon, andconducted4.

support more comprehensive conservation activities in theThe whitening phenomenon of woods was observed adjacent

future, investigations were conducted by in-situ and extra-situ

to metallic components in the Confucian Temple. In addition,

investigation

in-situin the restoration of 2011, several Nageshi (長押, a horizontal

investigations included microscopic observation, elemental

piece of timber to connect pillars) were substituted. Since

investigation and colorimetric measurements, extra-situ

then, the removed Nageshi were exposed to the rural

analysis included means of FTIR spectroscopy analysis,environment. After experiencing exposure for 3 years, traces

XRD analysis, SEM-EPMA, and IC analysis.

of copper components and the whitening phenomenon ofmethods.

Thenondestructive

adjacent wood were still clearly distinguishable. Therefore,
2. Study for the Confucian Temple of Kodokan of Mito

the removed Nageshi became an excellent object for

Table 1 Correlation coefficients (r) for I(Cu) and L* value for vertical window frames

学位論文梗概集 2016

sampling analysis while not harming the architecture itself

Table 2 Assignments of characteristic bands related to wood constituents

through the sampling process.
1) Nondestructive In-situ Investigation
The nondestructive in-situ investigations are microscopic
observation (Nikon Shuttle Pix P-400Rv), elemental
investigation (Bruker AXS, S1TURBO portable XRF device,
45s analysis time) and colorimetric measurements (Nippon
Denshoku Industries Co., Ltd, NF333, D65/10°). The
detected intensities of XRF analysis for each element wereapplied to represent the relative element concentrations ofevery investigation point in this research. The results ofcolorimetric measurements was summarized by the 1976
CIE L*a*b* equation, in which L* represents thelightness-darkness(+white,redness-greeness(+red,-black),-green),

a*represents

b*represents

yellowness-blueness (+yellow, -blue). The L* values wereselected to represent degree of whitening5.
Through microscopic observation for whitening areas,
whitish particles were observed in whitening wood, whereassome were not. Thus the type of whitening phenomenon
wereclassified

as“particle-attached”

typeand“no-particle-attached” type. The elemental investigation of
the wooden structures of sections with copper components
presented an inverse relationship between distance from

confirmed that a correlation between Cu contents and degree

cooper components and Cu contents. The relationshipof whiteness could not be simply concluded through a linear

between Cu contents and degree of whiteness were studied

relationship.

by calculating the correlation coefficients (r) for detected

2) Extra-situ Investigation

intensities of Copper (I (Cu)) and L* value of vertical

Before being removed, copper components were utilized towindow frames (Table. 1). In some sections, such as the No.

cover and decorate iron nails that connected pillars and5, No. 6 sections, the r values were close to 1, which suggest

Nageshi. After being exposed under the rural environment fora strong positive relationship between I (Cu) and L* values.

3 years, the parts once covered by the copper components

While in some parts, such as in parts of 7-WLL (r=0.6901),

could be easily distinguished according to clearly visible

7-WLR (r=0.5214), 7-WUR (r=0.5945), 9-WLR (r=0.7731),

traces, which matched exactly to the Nageshi copper

10-WLL

10-WUR

components, and its less degraded surface states. A(r=0.5840), the lower r values suggest relative weak positive

significant whitening phenomenon was observed in wooden(r=0.7022),

10-WUL(r=0.7415),
6

relationships between I (Cu) and L* values . In brief, it wasparts formerly adjacent to copper components while not inparts distanced from copper components.
To study the degradation characteristics of the different partsof in the removed Nageshi, 3 points were investigated by
nondestructive methods and sampling method respectively:
1) a point of the part formerly covered by copper components(RN-1 point), 2) a point of the part formerly adjacent tocopper components (RN-2 point), 3) a point of the part 6 cm
distanced from copper components trace (RN-3 point)

Fig. 1 Investigation points of the removed Nageshi(Fig.1).

Summaries of Academic Theses 2016

Table 3 Height ratios of absorbance bands of spectra for the RN-1, RN-2, RN-3 points

Table 4 I1336/I1317, the IR-CI, the XRD-CI, and the size of crystallite for the RN-1, RN-2, RN-3 points

Through nondestructive investigation for removed Nageshi,

and the size of crystallite can be calculated by X-ray

it was confirmed that whitening areas that were once adjacentdiffraction spectrum9.

to copper components contained higher Cu element, while noThe height ratio of I1336/I1317, the IR-CI, the XRD

particle attached on the wood tissues were observed.

Crystallinity Index (XRD-CI), and the size of crystallite areExtra-situ analysis included XRD analysis (Bruker AXS, D8

presented in Table 4. The Δ shown in Table 3 is theADVANCE/TSM,

percentage of variations of height ratios compared to the

40mV/40mA,0.5sec/step),

andFTIR-ATR analysis (PerkinElmer, Spectrum One(B), 4 cm-1

reference spectrum (RN-1).

resolution, 64 scans). Surface tissue samples were taken with

Results of FTIR and XRD analysis suggested that ina double blade razor without pretreatment.

whitening areas, which contained higher Cu elements,

Assignments of characteristic bands of FTIR spectra related

cellulose, hemicellulose and lignin were more severely

to wood constituents were conducted on the basis of previous

degraded, especially the latter two. The fact that acid

7,8

studies, and summarized in Table 2 .

treatments combined with accelerated thermal aging might

Chemical degradation of wood constituents (cellulose,result in a significant increase in the crystallinity index has

hemicellulose, and lignin) can be reflected by FTIR spectra.

been confirmed by some researchers 11 .An increase ofIn order to evaluate changes of characteristic bands related tocrystallinity relative to overall degradation of carbohydrate

wood constituents quantitatively，heights of characteristic

constituents implied that wood tissues of this area might havebands that assigned to wood constituents of FTIR spectra

experienced complicated more degradations and transitions

were ratioed with the selected internal reference, a band atof cellulose.

1030 cm-1. The results are shown in Table 3.
Since cellulose possesses both crystalline and amorphous

3. Study for the Old Iwasaki-ke Suehiro-bettei Villaregion, degradation of cellulose in wood can be evaluate byThe Old Iwasaki-ke Suehiro-bettei Villa is located atcrystalline portion. The height ratio of bands at 1336 cm-1

northwest of Tomisato City, Chiba Prefecture. It wasand 1317 cm-1 can decrease when the content of crystallized

constructed by Iwasaki Hisaya, who was the commander of

9cellulose increase . The height ratio of bands at 1423 cm-1

Mitsubishi Zaibatsu, at the beginning of Showa period forand 896 cm-1 can decrease, in the process ofdeveloping the agricultural industry in Tomisato City. As ade-crystallization, which is referred as the Lateral Orderreflection of upper-class lifestyle in the beginning of the10Indexes, or IR Crystallinity Index (IR-CI) . Besides, the CI
学位論文梗概集 2016

Showa period, the Main House (主屋), the Arbor (東屋), andFig. 3 Investigation points of the Main house(PerkinElmer, Spectrum One(B), 4 cm-1 resolution, 64
Fig. 2 Investigation point of the Arbor a) investigation points of exteriorpillar, b) investigation points of the Itakabe

Surface tissue samples were taken with a double blade razor

the Stone Storehouse (石蔵) were registered as Registration
In the Old Iwasaki-ke Suehiro-bettei Villa, the whitening
phenomenon of wood adjacent to metal components is
commonly observed, i.e., wood adjacent to the brass hinge ofthe shelf holders in Main House, the brass lamp bracket on
the exterior side of the pillar and the copper nails of thein-situ

investigations

aqueous extractives of the blade-razor-taken samples wereprepared for IC analysis. Each aqueous extractive sample
was prepared by immersing 0.40-0.50 mg of the original
sample, which was finely powdered by agate mortar, in 5 ml
ultra-pure water, incorporated with 10 min ultrasonicagitation.

exterior Itakabe (板壁, wooden wall) in the Arbor.
nondestructivefor XRD and FTIR-ATR analyses, and taken with carbon
tapes then coated with carbon for SEM-EPMA analysis. The

Tangible Cultural Properties of Japan in 201312 .

Thescans).

includedmicroscopic observation (Nikon ShuttlePix P-400Rv),
elemental investigation (Bruker AXS, S1TURBO portable
XRF device, 45s analysis time) and colorimetricmeasurements (Nippon Denshoku Industries Co., Ltd,NF333, D65/10°). Extra-situ analysis included SEM-EPMA(JEOL JXA-8530F, 15kV/50nA), XRD analysis (BrukerAXS, D8 ADVANCE/TSM, 40mV/40mA, 0.5 sec/step), ICanalysis (Methrohm 883 Basic IC Plus, 0.700 mL/min, 10.48
MPa, 40 min per measurement), and FTIR-ATR analysis

The following points of the Arbor were investigated (Fig. 2,Fig. 3): a whitening point adjacent to a brass lamp bracket on
the exterior side of a pillar (LB-W), a point 30 cm below theLB-W point as a normally weathered reference point(LB-Ex), a point in the interior side of the pillar as a barelyweathered reference point (LB-Int), a whitening point
adjacent to copper nail of the exterior Itakabe (CN-W), and apoint 10 cm below CN-W point as a normally weatheredreference point (CN-R). The pillar and the Itakebe of theArbor are made from cedar. In the Main House, points
around the brass hinge of a shelf holder in the pantry room

Table 5 The major results of in-situ investigation, XRD analysis and IC analysis for the Old Iwasaki-ke Suehiro-bettei Villa

Summaries of Academic Theses 2016

Table 6 Height ratios of the FTIR spectra for investigation points in the Old Iwasaki-ke Suehiro-bettei Villa

were investigated: a whitening point adjacent to the active

reference spectra (LB-Int for samples of the Arbor, H-R forside of hinge (H-W-1), a whitening point adjacent to the fixedsamples of the Main House samples).

side of hinge (H-W-2), and a point 10 cm to left of the active

Combine with the content of oxalate detected by the IC

hinge as a barely weathered reference point (H-R). The shelfanalysis in each sample, significantly varied bands of FTIR

holder was made from hinoki (cypress).

spectra for oxalate contained samples which could be figured

The major results of the in-situ investigation, XRD analysis,out by comparing Δ values, might provide clues aboutand IC analysis are summarized in Table 5.

sources of oxalate (While since intensity at 1030 cm-1 of theThrough microscopic observation, whitish particles wereH-W-2 point was shown a significantly decrease relative toobserved in some whitening wood (“particle-attached type”),

other characteristic bands, thereby height ratios for H-W-2

whereas some were not (“no-particle-attached type”). Only

shown less apparent Δ values of most bands).

particle-attached type was observed in the Arbor while bothResults of FTIR analysis suggested that in whitening areas,

the 2 types were observed in the Main House.

either

XRF analysis showed the high concentration of Zn and Cu inhemicellulose (bands at 1740 cm-1, 1160 cm-1, 1030 cm-1,

particle-attached whitening wood adjacent to brass and896 cm-1) and lignin (band at 1122 cm-1, especially syringyl

copper components respectively. Detected intensity of Zn innuclei related band at 1593 cm-1) constituents were moreparticle-attached type whitening area was extremely stronger

severely attacked than normally weathered areas. Compared

thanno-particle-attachedtype.

particle-attachedorno-particle-attached

type,

SEM-EMPA analysis

with no-particle-attached type, degradation of hemicellulose

incorporated with XRD analysis confirmed that attached

was more remarkable in whitening samples with attachedparticles might be predominantly formed by zinc or copper

particles. These suggest that the formation of oxalic acids

oxalate compounds corresponded to brass and copper

may be attributed to degradation of hemicellulose and lignin

components respectively. Through IC analysis, the significantof wood.

presence of oxalate, along with the presence of sulfate orchloride were also detected in whitening samples, especially

4. Conclusion

in samples of particle-attached type.

Oxalic acid is the simplest dicarboxylic acid with 3 main

Heights of characteristic bands that are assigned to wood

properties: a source of the proton, a source of the electron,

constituents of FTIR spectra were ratioed with the selected

and a strong metal chelator13. Oxalic acid commonly exists ininternal reference (band at 1030 cm-1). And Lateral Orderplants, and in biosynthesis products of many wood rot

Index (height ratio of bands at 1423 cm-1 and 896 cm-1) was

fungi14,15. It was firstly obtained from fusion of carbohydrates

also calculated (Table 6). The Δ shown in Table 1.2 is thewith sodium or potassium hydroxide1. In the field of paper

percentage of variations of height ratios compared to themaking industry, it has been discovered that significant oxalic

学位論文梗概集 2016

acids can be formed in the alkaline peroxide bleaching

References

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acids are formed from galacturonic and glucuronic acids,
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units relative to guaiacyl units form more oxalates16,17.
According to this, in the case of the Old Iwasaki-ke
Suehiro-bettei Villa, it is possible that oxalic acids were
produced by the degradation of hemicellulose and lignin
constituents in wood. Degradation of wood constituents,
especially the lignin units induce a whitish discoloration ofwood, namely the no-particle-attached type whitening
phenomenon of wood. Oxalic acid in wood, that presents
high metal content, act as a strong metal chelator. Oxalic
acids combine with the metal ions in wood, which migratefrom metallic components during the process of corrosion, toform metallic oxalate complexes. Precipitation of whitish
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should be formed. In wood associated with brass components,
the zinc oxalate should be formed for the preferential
degradation of zinc that is caused by the lower
electrochemical nobility of Zn than Cu.
Additionally, metal ions may play a vital role in production ofoxalic acids. However, the study for the Confucian Temple of
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and degree of whiteness was not simply linear. The
investigation of removed Nageshi shown that, no trace ofoxalate was detected in Cu highly concentrated wood. The
analysis for no-particle-attached whitening wood in the Old
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oxalates with insignificant Zn content. Results of IC shown
that, concentration of sulfate or chloride, which may
accelerate corrosion of metal, were detected concomitantwith oxalate in the whitening area. Therefore, it is highly
possible that the formation of oxalate in wood is affected bydiverse factors acting together, besides metal ions, such as analkaline environment.
Further studies are therefore necessary to investigate more
extensive cases and affecting factors to provide morecomprehensive understandings about this phenomenon, andultimately to develop the most appropriate combination plans
to deal with this phenomenon caused in cultural properties.

Summaries of Academic Theses 2016