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Journal of Cultural Heritage 11 (2010) 279–287

riginal article

esearch on protection of the architectural glazed ceramics in the Palaceuseum, Beijing

ing Zhao ∗, Weidong Li , Hongjie Luo , Jianmin Miaoncient Ceramics Research Center, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China

r t i c l e i n f o

rticle history:eceived 1st April 2009ccepted 27 May 2009vailable online 19 March 2010

eywords:alace Museum

a b s t r a c t

The main damage of architectural glazed ceramics in the Palace Museum was investigated and thephoto resistance, thermal resistance of protective materials as well as the protected performance suchas hydrophobicity, freeze-thaw resistance, bending and compressive strength of the polymer-appliedceramics was tested. The results showed the main damage of glazed ceramics was the shedding of glazelayer and the change of environmental water and temperature especially subzero was the main reasonfor the glaze shedding. The photo-resistant and thermal-resistant of protective materials fluorine resinand the compound materials composed mainly of the fluorine resin were better than Paraloid B72 and

rchitectural glazed ceramicslaze-sheddingrotection

the compound materials composed mainly of Paraloid B72. The wrapping method was selected for theprotection of glazed ceramics and the hydrophobicity, freeze-thaw resistance, bending and compressivestrength of the polymer-applied ceramics were improved, especially protected by fluorine resin and thecompound materials composed mainly of the fluorine resin. The optimum polymer could penetrate intothe damaged seriously glazed ceramics and play a hydrophobic role in the protection. The report will beuseful for the preservation of damaged seriously architectural glazed ceramics.

. Introduction

Seat of supreme power for over five centuries (1416–1911), thealace Museum in Beijing, with its landscaped gardens and manyuildings constitutes a priceless testimony to Chinese civilizationuring the Ming and Qing dynasties. These remarkable architec-ural edifice offer important historical testimony and fully embodyhe artistic features as well as present the emperor′s monarchicalower.

As symbolizing the supreme royal power of the emperor andhe emperor’s dignity, the yellow glazed ceramics were used exclu-ively on Palace Museum architecture and buildings (Fig. 1). Yellowlazed ceramic roofs used in the construction started in the Songynasty (960–1279) and in the Ming and Qing dynasties, it wasandated absolutely by the emperor and only be used in the con-

truction of the imperial tombs, imperial palace and altars. No otheruildings were allowed to use the yellow glazed ceramic roofs.

Apart for the emperor power symbol, artistic characteristics, the

lazed ceramics in the roof also have practical value such as water-roof and anticorrosion for the construction. But the long-termxposure in the atmospheric environment, the different damagesuch as glaze cracking, shedding and matrix powdering as well

∗ Corresponding author. Tel.: +86 21 52412372; fax: +86 21 52413903.E-mail address: zhaojing@mail.sic.ac.cn (J. Zhao).

296-2074/$ – see front matter © 2010 Elsevier Masson SAS. All rights reserved.oi:10.1016/j.culher.2009.05.004

© 2010 Elsevier Masson SAS. All rights reserved.

as other phenomenon happened [1]. If the indispensable artifi-cial interference and the optimum protective measures were notadopted, the precious value of these rare culture heritages woulddisappear forever.

So far many glazed ceramics on the buildings in the PalaceMuseum had to be replaced many times in different dynasties [2].In spite of the replaced glazed ceramics remained the original archi-tectural structure, the historical information and the authenticityof artifacts would not exist. Accordingly, the in-situ conservationfor the glazed ceramics in the Palace Museum would be urgent andimperative.

Currently, organic-coatings reported by many domestic and for-eign literatures [3–13] had been extensively used for protectionof some culture heritage such as ancient ceramics, stone heritage,frescos and so on, but less information concerned about protec-tive of glazed ceramics. The performance of six commonly usedprotective materials [Table 1] including Primal SF, Paraloid B72,organic-silicon, polyurethane, silicone-acrylic emulsion and fluo-rine resin were studied in our research paper [14], at the sametime, the blend of Paraloid B72 and fluorine resin at different pro-portion to be tested, the objective was to improve the properties

of Paraloid B72 in some extent and reduce the material cost. Theproperties such as color, tensile strength, acid and alkali resistance,water resistance, thermal degradation and photo degradation ofthese materials were tested, the results showed except for theproperties of fluorine resin, some problems such as color, water

280 J. Zhao et al. / Journal of Cultural Heritage 11 (2010) 279–287

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Fig. 1. Buildings

esistance and photoresistance in Primal SF, tensile strength andhotoresistance in Paraloid B72, the acid and alkali resistance inrganic-silicon, the color, water resistance, alkali resistance andensile strength in polyurethane, the color, tensile strength andhermal-resistance in silicone-acrylic emulsion had came forth. Asor the compound materials, the larger content of the fluorine resin,he better of the protective performance. Due to the space limit,uorine resin, a blend of fluorine resin and Paraloid B72 at propor-ion of 2:8 and 8:2 were used to compare with Paraloid B72 can bemployed as the protective materials for the architectural glazederamics conservation.

. Experimental

.1. Instruments

Eagle III energy dispersive X -ray fluorescence spectrometerEDXF, United States); D/max 2550 V X-ray diffractmeter (XRD,apan); NETZSCH 402E dilatometer (Germany); JSM-6700F SEMJapan); Xenon- lamp simulation test apparatus (China); JC2000Contact angle meter (United States); Universal testing instru-ent (Germany); Diffuse reflectance infrared spectrometer (United

tates); UV-vis spectrophotometer (Japan); AB-140N analyticalalance (Switzerland).

.2. Architectural glazed ceramics

The representative samples of architectural glazed ceramicsn Qing dynasty were selected from the buildings of the Palace

useum, the main damage of glazed ceramics was the shedding ofhe glaze layers (Table 2). The weathered seriously glazed ceramics

ut into pieces of approximately 35 × 35 × h mm3, where h is theeramics thickness.

The measurement was repeated three times and quoted as theverage value in each case. So, more than 300 pieces of samplesere involved in this paper.

able 1rotective materials.

Protective material Main components

Primal SF Methacrylate and methyl methacrylate copolymerB72 Methacrylate and ethyl methacrylate copolymerOrganic-silicon Silane and siloxane mixture

Polyurethane Aliphatic polyurethaneSilicone-acrylic emulsion Silicone-acrylate resins

Fluorine resin Fluoroethylene and alkyl vinyl ether copolymer

Compound 1 Paraloid B72: fluorine resin = 8:2Compound 2 Paraloid B72: fluorine resin = 2:8Compound 3 Paraloid B72: fluorine resin = 7:3Compound 4 Paraloid B72: fluorine resin = 6:4Compound 5 Paraloid B72: fluorine resin = 5:5Compound 6 Paraloid B72: fluorine resin = 4:6

Palace Museum.

2.3. Protective materials

The representative protective materials including Paraloid B72,fluorine resin and a blend of Paraloid B72 and fluorine resin at pro-portion of 8:2 and 2:8 to be applied in acetone and 10% solutionwere made. In order to monitor the change of protective materi-als in accelerated aging test, the film of protective materials wereperformed.

2.4. Methods

2.4.1. Glazed samples testEnergy dispersive X-ray fluorescence spectrometer (EDXF) pro-

vided a high-intensity small-spot analysis beam by using Rhtube (40 KV,40 W) and utilizing focusing 300 micron monocapil-lary optics was performed to identify the composition present inthe glaze and body of glazed ceramics.

The mineralogical composition of the ceramic matrix (crushedto powder in an agate mortar after removing the glaze) wasmade from X-ray diffraction (XRD) using CuK� (� = 1.5406 A◦)graphite-monochromatized radiation. Patterns were obtained bystep scanning from 10◦ to 70◦ 2�.

The samples prepared for testing the thermal expansion coeffi-cient including crush up the glaze to powder about 1 g and mouldfor the bands of 3 × 3 × 20 mm3 and fired at 1200 ◦C, the bodywas cut into the same size and tested each of samples. The ther-mal expansion coefficient was measured with a dilatometer in airatmosphere and the test temperature interval of RT-500-RT. Themeasurement was performed with a heating rate of 2◦/minute.

The tests of bulk density, water absorption and porosity inmatrix were made for each of the five samples, which measured

according to Chinese national standard GB/T3810.3-2006 [15].

2.4.2. Protective materials testIn the condition of thermal aging, the temperature was kept at

80 ◦C. The simulated photo-aging was performed in a simulation

Solvent/Dispersion agent Manufacture source

Water German companyAcetone German companyToluene Shanghai Renmai Engineering Material Co.,

Ltd, ChinaWater Jiangyin Guolian Chemical Co., Ltd, ChinaWater Shanghai Huasheng Polymer Material Co.,

Ltd, ChinaAcetone Shanghai Ofluorine Chemical Technology

Co., Ltd, ChinaAcetoneAcetoneAcetoneAcetoneAcetoneAcetone

J. Zhao et al. / Journal of Cultural Heritage 11 (2010) 279–287 281

Table 2Introduction of relic samples.

No. Volume (cm3) Glaze Matrix Signature Type

G1 35.5 × 18.0 × 9.0 About 90% off Well “Qianlong manufacture”

G2 34.0 × 15.0 × 8.0 About 50% off Small damage “Yongzheng 8 years manufacture”

G3 32.0 × 13.0 × 7.0 Shedding completely Well No

G4 37.5 × 16.0 × 9.0 About 25% off Well “Yizuoxu manufacture”

G5 34.0 × 14.5 × 8.0 About 95% off Well “Wuzuo manufacture”

G6 38.0 × 17.0 × 9.5 About 25% off Well “Qianlong manufacture”

G7 34.0 × 15.0 × 8.5 About 80% off Well “Yongzheng 8 years manufacture”

G8 33.0 × 14.0 × 6.5 More than 70% off Well “Sanzuo manufacture”

G9 26.0 × 13.0 × 8.0 Shedding completely Weak No

282 J. Zhao et al. / Journal of Cultural Heritage 11 (2010) 279–287

Table 3Major and minor element composition of glazed ceramics (wt%).

Formula Glaze Matrix

G1 G2 G3 G1 G2 G3

Na2O 0.52 0.58 0.78 1.50 1.16 1.33MgO 0.25 0.12 0.22 0.41 0.82 0.84Al2O3 5.74 3.85 4.72 29.69 28.27 25.72SiO2 33.49 29.73 29.38 60.78 60.44 63.10K2O 0.91 0.49 0.59 3.51 2.78 3.43CaO 0.46 0.34 0.43 0.64 1.94 1.05

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TiO2 0.5 0.52 0.53 0.73 0.75 0.57FeO 2.8 2.49 2.03 1.74 2.83 2.96PbO 55.33 61.88 61.32

est apparatus equipped with a Xenon lamp of average irradiance50 W m−2, the temperature was kept at 50 ◦C and the relativeumidity (RH) was kept constant at 43%.

The changes of molecular structure and transmittance of pro-ective material films in photo-aging and thermal-aging wereeparately investigated by the diffuse reflection spectrometer withn ATR accessory and UV-vis spectrophotometer.

.4.3. Glazed samples protectionUsing the immersion method as for the glazed ceramics in

arge architectural building was not as much as possible duringhe in-situ protection. So the other protective methods were to beonsidered:

spraying method: A water-can used well-proportioned for spray-ing the protective material on the surface of the glazed ceramics.Record the spraying times until the protective material was notto be absorbed, and about 2 to 3 mm of solution was used for apiece of sample;brushing method: A brush dunking the protective material wasused directly on the surface of glazed ceramics and the amountof solution as much as that in spraying method;wrapping method: After the glazed ceramics were wrapped bycotton cloth or gauze, the protective material was separatelysprinkled by the water-can or brushed on the surface of the wrap-page. The amount of solution was about 10 to 15 mm for a pieceof sample.

Samples were observed before and after protection under scan-ing electron microscope (SEM) using electron secondary beamst 15 kV. Images acquired by electron microscopy allowed theicrostructural characterization of the ceramics with the evalu-

tion of the pore fraction.To evaluate the bending and compressive strength of treated

nd untreated ceramics, three tests were made for each of the five

amples before and after the protection. The tested samples wereut into 20 × 10 × 10 mm3 and 10 × 10 × 10 mm3 respectively own-ng to the limit of camber in the glazed ceramics. The tests were

ade in a universal testing instrument and the cross-head speedas 0.5 mm min−1.

able 4hermal expansion coefficient and the physical properties of glazed ceramics.

Serial number Thickness/um Thermal expansion coefficient

Glaze G4 90 ∼ 200 (uneven) 6.37 ± 0.29Matrix G1

G2G3G4 5.50 ± 0.41G9

Fig. 2. XRD diagram of architectural glazed ceramic G1.

3. Results and discussion

3.1. Main damage analysis

Considering the specialty of the weathered seriously glazedceramics, the internal and external reasons for the damage wasinvestigated.

3.1.1. Internal reasonTake the G1-G3 as an example, Table 3 showed the major and

minor element composition of glaze layer and matrix in glazedceramics, the major element composition of glaze layer was PbO,SiO2, and the matrix was SiO2, Al2O3. Fig. 2 was the result of XRDin body of glazed ceramics G1, the crystal phase of matrix mainlyhad �-quartz, mullite, plagioclase and calcite. The measurementresults of the other glazed ceramics were consistent with that ofG1. This information provided the preliminary knowledge for theglazed ceramics of Qing dynasty in the Palace Museum.

Table 4 showed the thermal expansion coefficient in glaze layerand matrix. Owning to the thermal expansion coefficient in leadglaze layer is greater than that in matrix, the crack happened inthe lead glaze layer during the process of glazed ceramic making.As Fig. 3, the crack distribution of glaze layer in G4 for example,these cracks distributed as a decorative pattern in the turtleback,which was called “ice crack” in China, they staggered and someeven extended to the whole surface of glaze layer. In cross sectionalmicrostructure, some even crossed the glaze layer and directly tothe matrix (Fig. 4). The “ice cracks” formed the channel for the out-side water from the glaze layer inflow into the matrix, which wouldaffect the waterproof of the glaze layer to a certain extent.

The physical properties of glaze layer and matrix in glazedceramics were different, such as the water absorption in glaze layerwas nearly to zero [16], whereas that in matrix was more than 15%(Table 4). In order to analyze the relationship between the residualglaze layer and the water absorption of matrix, abundant glazed

× 10−6 (500 ◦C) Physical properties

Bulk density(g cm−3)

Water absorption (%) Apparentporosity (%)

– – –1.88 ± 0.02 15.10 ± 0.23 29.00 ± 0.551.75 ± 0.02 19.60 ± 0.64 34.00 ± 0.871.87 ± 0.01 15.00 ± 0.13 28.00 ± 0.001.88 ± 0.01 15.20 ± 0.13 28.00 ± 0.551.79 ± 0.01 17.70 ± 0.07 32.00 ± 0.45

J. Zhao et al. / Journal of Cultural Heritage 11 (2010) 279–287 283

Fig. 3. Crack distribution of glaze layer in G4.

Fig. 4. Longitudinal cracks of glaze layer in G4.

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Table 5Environment monitoring data of the Palace Museum in 2002.6–2003.7 [8].

Time Temperature( ◦C) Relative humidity (%)

Average Highest Lowest Average Highest Lowest

2002.6 24.6 37.2 13.6 63.0 100.0 15.02002.7 28.5 41.8 20.6 67.0 100.0 14.02002.8 27.2 37.1 19.0 70.0 100.0 12.02002.9 22.0 37.5 13.3 63.0 100.0 16.02002.10 12.2 24.8 −2.1 52.0 100.0 11.02002.11 4.7 14.2 −3.4 47.0 100.0 14.02002.12 0.2 8.7 −13.5 65.0 100.0 14.02003.1 −0.2 13.5 −9.8 39.0 100.0 11.02003.2 2.5 14.6 −6.9 53.0 100.0 17.02003.3 7.4 22.7 −1.0 59.0 100.0 16.0

The detect of atmosphere environment used segment indexsuch SO2, NO2, O3, F− and TSP as selected factors, the results(Table 6) indicated except the average concentration of TSP washigher than II standard of national pollution index (Table 7), whichrepresented the safe environmental quality index for cultural her-

Table 6Detected value of atmospheric environmental pollutants in Palace Museum(units:mg/m3).

Time Pollutants

SO2 TSP NO2 O3 F H2S

1998.6 0.024 0.373 0.044 0.085 1.224 0.0041998.7 0.010 0.272 0.064 0.064 0.686 0.0031998.8 0.013 0.269 0.041 0.029 0.746 0.0031998.9 0.032 0.312 0.045 0.045 0.840 0.0021998.1 0.034 0.503 0.105 0.029 0.636 0.0021998.11 0.065 0.247 0.082 0.017 0.710 0.0041998.12 0.279 0.378 0.082 0.037 1.314 0.0041999.1 0.104 0.433 0.040 0.025 1.630 0.0031999.2 0.162 0.318 0.064 0.010 1.278 0.0041999.3 0.083 0.513 0.062 0.006 0.822 0.0041999.4 0.021 0.718 0.053 0.019 0.570 0.0031999.5 0.007 0.462 0.044 0.026 0.774 0.003

Table 7National air environmental quality standard for the least value of common pollutantconcentration.

Pollutant Concentration detection limit

Level standards 2 standards 3 standards Units

3

ig. 5. Relationship between the residual glaze layer and the water absorption ofatrix.

eramics were studied and the result was reported in Fig. 5: whenhe residual rate of glaze layer kept below 20%, the water absorp-ion of matrix entirely more than 13%, while the glaze layer keptlmost intact, the water absorption of matrix below than 13%, thats, the order of percentage about water absorption of matrix directlyffected the condition of the glaze layer and the water absorptionf matrix below than 13% would help for the remained intact of

laze layer.

Carefully observing the dropout position of glaze layer almostt the latter half part of glazed ceramics (Table 2), where the glazeayer thicker, that was, crack happened easily in the thicker glaze

2003.4 16.3 31.4 6.1 50.0 100.0 13.02003.5 22.1 33.4 11.0 62.0 100.0 16.02003.6 25.5 36.8 14.8 58.0 100.0 17.02003.7 26.9 40.5 18.4 71.0 100.0 19.0

layer during whole surface which changed from 90 to 200 microns(Table 4).

In all, the mismatch of thermal expansion coefficient and waterabsorption between glaze layer and matrix, as well as differentthickness glaze layer provided the potential condition for damageof glazed ceramics.

3.1.2. External reasonThe outdoor environment also played a great role in the damage

of the glazed ceramics. Table 5 was the investigation of envi-ronment monitoring data including RH and temperature of thePalace Museum in June 2002 to July 2003 [17], which showed theRH in January 2003 up to 100 percent and the lowest 11 percent,the temperature reached 13.5 ◦C highest and the lowest subzero9.8 ◦C.

SO2 0.05 0.15 0.25 mg/mTSP 0.12 0.30 0.50NO2 0.08 0.08 0.12O3 0.16 0.20 0.20F 1.80 ug/dm2 d

284 J. Zhao et al. / Journal of Cultural Heritage 11 (2010) 279–287

Table 8Condition and results of simulation test for the shedding of glaze layer.

Serial number Experimental conditions Before experiment After experiment

180 h (30 cycles) 378 h (63 cycles) 3600 h

1 110 ◦C No change

2 −30 ◦C No change

3 30 ◦C, saturated No change

4 110 ◦C, −30 ◦C, 3 h per cycle No change

5 25 ◦C saturated, −30 ◦Cfreezing, 3 h per cycle

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6 100 ◦C saturated, −30 ◦Cfreezing, 3 h per cycle

tage, the other indexes were still within the II standard, that’s, thecid pollutants such as SO2 and NO2 had no significant effect foramage of the glazed ceramics.

.1.3. Simulation testThe similar composition, structure and thickness modern glazed

eramics were selected for simulating the damage of ancientlazed ceramics. The experimental conditions and results showedn Table 8. Number 1, 2 and 3 was respectively the single conditionnd the Number 4, 5, 6 were the cycling condition. Number 4 wasigh-low temperature cycling test, Number 5 was the freeze-thawesistance cycling, test was according to the Chinese national stan-ards for architectural colored glaze products, including immersehe products in water for 3 h at 20-25 ◦C, freezing 3 h at −4 to −10 ◦Cfter removing sample out of water, and then immersed sample intoater again for 3 h, record the cracks of products in this repeated

ycle. The different between Number 6 and Number 5 merely washe higher temperature in immersed water.

The results showed each single factor such as high temperature,ow temperature or water as well as high-low temperature cycle

ithout water was no effect on damage of glaze layer. Whereashe crack of the glaze layer happened at 63 cycling in the freeze-haw resistance of Number 5, indicated the “ice crack” extendedwning to the mismatch of volume expanded after water uptake inlaze layer and matrix on the process of high-low temperature cycleaving water, which made the interfacial binding force between

laze layer and matrix was affected, would lead to the glaze layerhedding off when the interfacial binding force decreased a certainxtent. The result of Number 6 showed the crack happened ear-ier at the immersed water temperature rose in the freeze-thawesistance.

3.1.4. The main reason analysisThe matrix of glazed ceramics absorbed much water after rain-

fall as for the water absorption in matrix was more than 15%.Especially in winter, the temperatures below zero, the matrix vol-ume expanded at the time of the absorbed water turned into ice.Adversely, the matrix volume contracted at the ambient temper-ature rose and the ice melted. Owning to the cycling in volumeexpanded and contracted of matrix, the interfacial stress betweenglaze layer, which volume kept invariant because of hydrophobicproperty, and body was enhanced, would decreased the bindingforce between glaze layer and matrix as far as the glaze layer shed-ding off.

In conclusion, the mismatch of thermal expansion coefficientand water absorption in glaze layer and matrix as well as uneventhickness glaze layer provided the internal condition for damagedglazed ceramics. The changes of environmental water and tem-perature especially subzero were the main external reason for thedamage of glazed ceramics.

3.2. Protective materials

It was difficulty to revise the consistent of thermal expansioncoefficient in glaze layer and matrix as well as the thickness ofglaze layer for protecting the damaged glazed ceramics. An effectivemethod was to decrease the water absorption of matrix by append-ing some excellent protective materials, which would be improving

the durability of the glazed ceramics.

Diffuse reflectance infrared spectroscopy is an in-situ techniqueused to detect the molecular framework of protective materials[18,19]. Owning to the main degradation happened in the surfaceof materials, diffuse reflectance infrared spectroscopy was picked

J. Zhao et al. / Journal of Cultural Heritage 11 (2010) 279–287 285

Fig. 6. Spectra of B72 and compound 1 before irradiation.

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Fig. 8. Spectra of the compound 2 and fluorine resin before irradiation.

Fig. 7. Spectra of B72 and compound 1 investigated after 288 h of irradiation.

s a monitor in tracking the chemical change and degradation ofroducts during the degradation period [20].

.2.1. Photo degradationThe infrared spectrum of Paraloid B72 and compound 1 were

imilar before degradation (Fig. 6). Paraloid B72 was the methacry-ate and ethyl methacrylate copolymer, the change of structureFig. 7) happened at the main absorption peak 3000 ∼ 3600 cm−1OHnd 1758 cm−1 C = O, which, due to the generation of lactones andlcohol, the reaction equation was as following:

The decrease of 2969 cm−1CH3, 2877 cm−1�s(CH2),481 cm−1�(CH2), 1295 cm−1, 1045 cm−1�(C-O-C) inferred theracture of side chain in Paraloid B72. The distinction of com-ound 1 between Paraloid B72 was the different decline rate inhe main characteristics absorption bands. The average changef main absorption peaks C = O and �(C-O-C) in compound 1 andaraloid B72 was separately 0.02%·h−1 and 0.1%·h−1 by means ofalculation.

The strong and sharp spectrum peak appeared at 1265 and−1

153 cm in the infrared spectrum of fluorine resin (Fig. 8), which

as the stretching vibration characteristics peak of C-F bond. Theavenumber of 975 cm−1, 1789 cm−1was the C-Cl, C = O absorptioneak, and the 1396 cm−1 was the variable-angle vibration of C-Hond, which was the -CH3 and -CH2 of alkyl vinyl ether monomer.

Fig. 9. Transmission curve for fluorine resin at 94.5-h thermal-ageing.

Comparing the infrared spectrum of fluorine resin and com-pound 2, the spectrum peak broaden at 1789 cm−1, which wasthe bond C = O of acrylic acid. The peak transferred to highwavenumber and decreased at 1153 cm−1. The intensity of C-O-Cin 1045 cm−1 increased as the coincidence of bond C-O-C in acrylicacid and C-F in fluorine resin.

Nearly no change happened in main absorption peaks of fluo-rine resin and compound 2 at 288-h photo-aging, better than othermaterials.

3.2.2. Thermal degradationThe transmission curve of the protective materials in ther-

mal aging was tested by UV-visible spectrophotometer. Generallyspeaking, the transmittance of protective polymer film was closeto 100%, which would be decreased under the high temperatureageing at the polymer structure changed, especially in short wave-length region. In short, the fewer decrease transmission coefficient,

the less change polymer structure, and the better polymer thermalstability. As the transmission curve for fluorine resin (Fig. 9) andcompound 2 (Fig. 10) in thermal aging for example, the transmis-sion curve decreased and the average change ration of transmissioncoefficient in both materials were less than 2% at 420 nm in 94.5-

286 J. Zhao et al. / Journal of Cultural Heritage 11 (2010) 279–287

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cultural heritage was the effective convergence of polymer materi-als and the combined degree between polymer and cultural matrix.

Fig. 10. Transmission curve for compound 2 at 94.5-h thermal-ageing.

ageing. Compared with the change of other materials such asilicone-acrylic emulsion, these four materials had less changeation and well thermal stability.

.3. Glazed ceramics protection

Polymers were applied for architectural glazed ceramics espe-ially the damaged seriously ceramics like G9 in order to enhancehe hydrophobicity, the freeze-thaw resistance and mechanicaltrength of matrix.

.3.1. Protective methodThe glossiness surface changed especially in the edge of glazed

eramics when used the spraying method and brushing method forrotection, although the concentration of the polymers decreasedt 2%, whereas no change in the surface by wrapping method at0% concentration of polymers. Thus, the wrapping method waselected for the protection of weathered seriously glazed ceramicsn the following tests.

.3.2. HydrophobicityThe hydrophobicity of protected weathered seriously glazed

eramics was characterized by the measurement of contact angles.ig. 11 showed the contact angle in untreated matrix up to zero,hich means no water-repellent property of damaged seriously

lazed ceramics. After treated, the contact angle in glazed ceramicsere enhanced and especially treated by fluorine resin and com-ound 2, up to 80◦.

.3.3. Freeze-thaw resistance

Freeze-thaw resistance is an important indicator for inspecting

he performance of damaged seriously glazed ceramics in the Palaceuseum. Test was according to the Chinese national standards for

rchitectural colored glaze products. At the end of two cycle, someatrix powder can be seen in water and the cracks happened in

Fig. 11. Contact angle change for the body protected by different materials.

Fig. 12. Bending strength of glazed ceramics protected by different materials.

the surface of unprotected glazed ceramics, while the protectedproducts remain integrity at the end of 15 cycles.

3.3.4. Bending and compressive strengthOn the important condition of standard deviation below 1.00,

Figs. 12 and 13 showed the arithmetic average value in bendingstrength and compressive strength, respectively, increased with thetreatment. This was most probably a direct effect of the reduction inporosity due to treatment, which in the case of these samples ledto considerably smaller pore size fraction than that unprotected.However, it must be stressed that the treatment and the relatedreduction of the porosity are not the only factors that affect thebending and compressive strength. For example, the presence ofcracks and their propagation during the tests also influence themechanical behavior of the samples.

3.4. Protection mechanism analysis

SEM analysis was adopted for studying the combination inprotective materials and the protected cultural heritage particles.Fig. 14 as the SEM micrographs of the cross-section in the untreatedceramics and the one protected by fluorine resin for example, inwhich can be see the resin was penetrated into inner of inorganicmatrix and most pores were filled, the three-dimensional networkstructure was come into being after solvent evaporation and theresin solidified, which played the reinforce and support role ineffective enhanced matrix strength.

Polymeric material fills the pores of the relic mineral matrix,forming a quite continuous coating that links up the inner wallsof the pores through physical interactions. The key to the preserve

The binding force in weathered seriously cultural relic particles wasenhanced by infiltrating the excellent property polymers. At thesame time, the water absorption of the body was decreased from

Fig. 13. Compressive strength of glazed ceramics protected by different materials.

J. Zhao et al. / Journal of Cultural Heritage 11 (2010) 279–287 287

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Fig. 14. SEM micrographs of (a) untreated gl

7.7 to 8.7% and 9.0% treat by fluorine resin and compound 2, whichould directly influence the interfacial stress between glaze layer

nd the matrix.

. Conclusions

The change of environmental water and temperature especiallyubzero was the main reason for the damage of glazed ceramics.

The photo-resistant of fluorine resin and compound 2 materialss well as the thermal-resistant of four materials were all good.

The wrapping method was selected for the protective of dam-ged glazed ceramics.

The hydrophobicity, freeze-thaw resistance, the bending andompressive strength of the polymer-applied ceramics weremproved, especially protected by the fluorine resin and the com-ound materials composed mainly of the fluorine resin.

Polymeric material fills the pores of the relic mineral matrix,orming a quite continuous coating that links up the inner walls ofhe pores through physical interactions.

The results obtained allow us to conclude that, in general,sed in wrapping method accomplishes its objectives, that is, theeathered seriously glazed ceramics possess higher mechanical

esistance and the biscuit gains hydrophobic characteristics obvi-usly protected by fluorine resin and the compound materialsomposed mainly of the fluorine resin. The report will be use-ul for the preservation of damaged seriously architectural glazederamics.

cknowledgements

This work was financially supported by the Science and Tech-ology Supporting Project (No. 2006BAK31B02) and the Nationalatural Science Foundation of China (No.50872143). The authorsratefully thank the Palace museum for kindly supplying the dam-ged seriously glazed ceramics.

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