Journal of Materials Science & Technology 32 (2016) 182–188

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Journal of Materials Science & Technology

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Ink Dispersion on Qianlong Xuan with Improved Ink Expression

Shuyi Wu 1, Xinglong Wu 1,*, Paul K. Chu 2

1 Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, 2 Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China

ARTICLE INFO Qianlong Xuan paper, lost two hundred years ago, was reproduced by engineers in Red-Star Xuan Paper Article history: Limited Liability Company of China. Its remarkable performance and profound historical value are highly Received 25 January 2015 regarded by artists and the paper commands very high price in the commercial market. Ink penetrates Received in revised form and spreads optimally in the paper and the words exhibit clear edges with small fluctuations because 11 July 2015 of the desirable wettability and wicking. These characteristics make it stand out from three Xuan paper Accepted 12 July 2015 samples. The good wettability, verified by contact angle measurements, is an essential prerequisite to Available online 17 December 2015 strong wicking. Attenuated total reflectance Fourier-transform infrared spectroscopy is performed to de- termine the chemical structure of Qianlong Xuan paper and the relatively large hydrogen bonding ratio Key words: contributes to the hydrophilicity. The microstructure investigated by scanning electron microscopy and Qianlong Xuan paper atomic force microscopy reveals wide fibers and a uniform fiber arrangement with good connectivity, Wettability dense network, as well as rough fiber surface. These unique properties endow Qianlong Xuan paper with Homogeneity Wicking strong wicking to improve the ink expression. & Surface roughness Copyright © 2015, The editorial office of Journal of Materials Science Technology. Published by Elsevier Limited. All rights reserved.

1. Introduction procedures and more than one hundred operations taking one to two years. Pulping is an essential process utilizing the stream in Jing Xuan paper, also called in Japan, is used widely in tra- County. Japan has used the same craft to produce Xuan paper but ditional calligraphy and painting and is a prominent type of Chinese the properties are not as good as those produced in the Jing County. handmade paper. It has been widely popular with calligraphers and It is believed that the water in the stream affects the quality of the painters since its inception in the (618–907 AD). Pro- paper. gressive calligraphers are always on the quest to show their Xuan paper underwent large development in the Qing Dynasty expression, which cannot be achieved without Xuan paper and in peaking in the period of Qianlong after its advent[2]. Emperor fact, good Xuan paper makes the arts more impressive. Qianlong, skilled in writing, was deeply in love with Xuan paper. Xuan paper manufactures are scattered all over the country. Red- The Qianlong Xuan paper that belongs to Tejingpi is the ultimate star , located in Jing County, Anhui Province, China, is one writing and painting paper. In order to attract more attention to Xuan of the best and Jing County is believed to be the home of the Xuan paper, Xing Chunrong, the chief engineer of the mill, reproduced paper, where the “traditional handicrafts of making Xuan paper” the Qianlong Xuan paper that was lost two hundred years ago by is listed as a UNESCO World Intangible Cultural Heritage[1]. collecting the related literature. The Qianlong Xuan paper, made by Xuan paper is made of pulped fibers of blue sandalwood bark the best engineer in one of the best Xuan paper companies, has and rice straws. According to different raw material ratios, Xuan paper immense historical significance, rarity and unmatched perfor- is classified into three types, Tejingpi, Jingpi, and Miaoliao, in which mance and owing to the limited supply, it commands the highest the ratios of wingceltis bark are more than 80%, no less than 60%, price. The outstanding wetting properties of Qianlong Xuan paper and about 40%, respectively. In general, the ink expression is better are determined by the chemical constituents and physical struc- for a larger ratio of the bark fibers. The production of Xuan paper ture, which are closely related to the raw materials and the uses natural materials and reagents and manual tools but the process manufacturing process and it is important to understand the sci- is complex and varies with different manufacturers. Normally, the entific reasons for the outstanding performance. production of traditional paper from raw materials requires 18 In recent years, there has been widespread investigation in ink dispersion on Xuan paper in the computer graphics community. However, ink dispersion is a complex phenomenon that involves * Corresponding author. Ph.D.; Tel.: +86 25 83686303; Fax: +86 25 83595535. the interplay between paper, water and ink constituents, thus making E-mail address: [email protected] (X. Wu). accurate physical simulation difficult. Moxi[3] simulated ink dispersion http://dx.doi.org/10.1016/j.jmst.2015.12.014 1005-0302/Copyright © 2015, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited. All rights reserved. S. Wu et al. / Journal of Materials Science & Technology 32 (2016) 182–188 183 in absorbent paper by adopting the Lattice Boltzmann Equation (LBE) 2.2. Ink dispersion experiments method, but they neglected the effects of the paper structure on the actual process. Moreover, in many statistical physics experiments Calligraphers wrote on the three types of paper under the same on liquid transport in porous media, paper is chosen for obvious conditions, for instance, same brush, same ink density, same speed and simple practical reasons. However, scientific research in wetting and style. In order to gain further insights into the effects of ink dis- of traditionally handmade Xuan paper has been scarce, except Liu persion under the controlled conditions, the ink with the same and Hu’s report on the wetting property of Chinese ink on Xuan volume of 50 μL is dropped onto the three types of from the paper[4] in 1984 and Wu’s study on the relationship between the same height of 1 mm. production technique and performance of ink embellishment on Chinese Xuan paper[5]. However, both of them did not pay enough 2.3. Characterization attention to the physical mechanism. Because of the lack of good understanding and considering the lofty status of Qianlong Xuan The contact angle measurements were performed on the OCA200 paper in Chinese arts and civilization, we want to unravel why (Dataphysics, Germany), FTIR spectroscopy was conducted on a Qianlong Xuan paper is so remarkable from the scientific perspective. Nicolet Nexus 870 spectrometer, scanning electron microscopy was carried out on the Hitachi S4800 scanning electron microscopy (SEM), 2. Experimental and the roughness of the fiber surface was assessed by AFM (AFM, NanoScope IV NS4-1). 2.1. Paper samples and preparation 3. Results and Discussion Two other kinds of high-quality Xuan papers, Jingpi and papers, are chosen for comparison. The Qianlong Xuan paper and 3.1. Ink dispersion effect Jingpi were provided by Red-star paper mill in Jing County, and Bamboo paper was purchased from a local Xuan paper agent. The In , artists utilize flexible brushes to create paper was cut into 6 cm × 3 cm, 1.5 cm × 1.5cmand6cm× 6cm expressive strokes. Fig. 1(a–c) shows three Chinese characters, Wu pieces for contact angle measurements, scanning electron micros- Chien-Shiung, a distinguished experimental physicist as well as an copy, and attenuated total reflectance Fourier-transform infrared honorable graduate of Nanjing University (originally Central Uni- (ATR-FTIR) spectroscopy, respectively. The specimens were placed versity). No ink is added until the first two characters are completed. in an oven at 60 °C for 6 h to ensure complete water evaporation. It should be noted that the spreading of ink can be fully shown when The tested pieces weighing 0.2 g were put in 60 mL of deionized the ink in the brush is rich. The first and third characters show better water under magnetic stirring at a low speed for 8 h to separate the wetting with the characters written as soon as the ink is added on fibers while not damaging them. Afterwards, the suspension con- Qianlong Xuan paper. Moreover, the second character looks driest taining the fibers was diluted with adding 200 mL of deionized water indicating that a great deal of ink has been consumed during the and the diluted suspension was dripped onto slides and silicon chips writing of the first character, meaning that the pressure between for fiber width and atomic force microscopy (AFM) measurements the outer edge of the ink front and beneath the brush tip is larger separately. than the capillary suction pressure formed by voids between brush

Fig. 1. (a, b, c) Front (left) and back (right) sides of Professor Fang’s work and (d, e, f) enlarged views of the edge of the scanned images of the ink dispersion (inset) on Qianlong, Bamboo and Jingpi Xuan paper, respectively. The scale bar is 1 mm. 184 S. Wu et al. / Journal of Materials Science & Technology 32 (2016) 182–188

Fig. 2. Photographs showing the water droplet shape on Qianlong (a), Bamboo (b) and Jingpi (c) Xuan paper, respectively.

hairs. Considering the competition between the two kinds of pres- 3.3. Chemical constituents sure, it is certain that capillary effects affect the ink dispersion more significantly on Qianlong Xuan paper. The back of the artwork is also The wettability, which plays an important role in the paper, demonstrated on the right, showing that Qianlong Xuan paper has depends on both the chemical composition and geometric micro- better performance of transverse wicking, which makes the ink flow structure of the surface[7] and so the chemical composition is studied. in the paper to vividly pick up the special charm of ink dispersion. Plant fibers are composed of , hemicelluloses, , pectin In order to gain further insights into the effects of ink dispersion and wax substance, among which cellulose is recognized as the major under the controlled conditions, the ink with the same volume of framework component of the fiber structure. Cellulose, a linear1,4- 50 μL is dropped onto the three types of papers from the same height β-glucan polymer, contains three hydroxyl groups and consists of both of 1 mm. For the low-density ink, the Weber number is given by amorphous and crystalline domains in varying proportions. In the crystalline regions, there are two hydroxyl groups that form hydro- = ργ (1) Wrghe 2 , gen bonds within the cellulose macromolecules while the rest interacts with other cellulose molecules through hydrogen bonding[8]. It reduces where ρ is the density, r is the radius, g is the gravitational con- the accessibility of hydroxyls to the reagent. Most of the reactants stant, h is the height of free fall and γ is the surface tension of the penetrate only the amorphous regions on the surface of the crystal- drop. Taking typical values of ρ = 1000 kg/m3, r = 10−3 m, g = 10 m/ lites with a low level of order. Hence, the crystallinity of cellulose s2, h = 10−3 m, and γ = 3 × 10−2 N/m, W is on the order of 1, much e plays an important role in the water absorption characteristics. smaller than 50, and no splashing occurs[6]. ATR-FTIR spectroscopy is one of the most useful methods to de- The scanned images of the ink dispersion are exhibited in termine the surface composition without complex sample Fig. 1(d–f) as insets and the boundary on Qianlong Xuan paper looks preparation and is used to study the hydroxyl groups and surface smoother. The spreading area is 24.5, 22.7, and 19.6 cm2 from left chemical bonding. As shown in Fig. 3(a), in the fingerprint region, to right confirming best spreading on Qianlong Xuan paper. The en- the characteristic bands at around 1040 cm−1 are assigned to the larged views of the edges monitored by optical microscopy also cellulose[9] and the broad band of OH-stretching vibration at 3000– demonstrate high contrast because except Qianlong Xuan paper, the 3650 cm−1 is observed from all the spectra[10], indicating that cellulose edge cannot be seen clearly on the two other samples at low con- is the main composition in the three types of paper. The enlarged trast. Meanwhile, it is obvious that the edge has small fluctuations, vibration bands in the fingerprint region are presented in the inset which display delicate tones better. Above all, the better wettability, of Fig. 3(a). Except the main band of the cellulose at 1050 cm−1, the transverse wicking, and longitudinal wicking make Qianlong Xuan bands at 986, 1031, 1106, and 1158 cm−1 can be assigned to C—O paper better than the other papers. vibration at C(6), C—O stretching, ring asymmetric valence and C—O—C asymmetric vibration from β-glycosidic link in cellulose 3.2. Wetting related to contact angle II[11,12], respectively. Moreover, the band at 3341 cm−1 corresponds to O(3)H. . .O(5) intra-molecular hydrogen bond[13]. Because there Wetting is a process in which a fiber–air interface is displaced is no much difference in the characteristic bands of cellulose, the with a fiber–liquid interface. Fiber wettability is a prerequisite to bands in the range of 900–1200 cm−1 are chosen for the hydroxyl the occurrence of absorption and penetration. Wetting of paper, a content determination. As shown in Fig. 3(b), the ratios of the in- fibrous assembly, is a complex process. The contact angle is useful tegrated intensity of OH-stretching vibration band at 3000– in characterizing wetting. However, it is difficult to measure contact 3650 cm−1 to the characteristic vibration band at 900–1200 cm−1 are angles on heterogeneous and porous paper, since water will pen- 1.25, 1.12 and 0.96, respectively, for Qianlong, Bamboo and Jingpi etrate the underlying and it will take some time for the Xuan paper, demonstrating that the hydrophilicity of Qianlong Xuan drop to stabilize geometrically. Hence, the drop volume is chosen paper is strongest. Furthermore, the “total crystalline index” (TCI), to be 4 μL and the measurement takes 0.02 s after impact, which the ratio of the two bands between 1372 cm−1 (C—H bending) and is the best compromise between geometric instability and onset of 2900 cm−1 (C—H and CH2 stretching) is used to measure the absorption. Considering the influence of various factors such as the crystallinity[14], which is 1.04, 1.06 and 1.14, respectively, for Qianlong, surface roughness, chemical heterogeneity, and so on, the contact Bamboo and Jingpi Xuan paper, and hence, water gets access to the angles were measured repeatedly from two hundred different po- hydroxyls comparatively easily on Qianlong Xuan paper. Water mol- sitions on each paper. The results are presented in Fig. 2. The average ecules interacts with hydrophilic groups by hydrogen bonds to values are as follows: 36.8° on Qianlong Xuan paper, 50.1° on Bamboo improve the surface hydrophilicity and water will enter and fill the paper and 60.6° on Jingpi. The wettability of Qianlong Xuan paper grooves of the fiber network due to the capillary effect that results is the best thus bonding well for absorption and spreading. in the enhanced hydrophilicity. S. Wu et al. / Journal of Materials Science & Technology 32 (2016) 182–188 185

Fig. 4. Variation in the contact angle as a function of time on the three paper samples.

formed on ten replicates for each type of paper. The contact angles decrease most rapidly on Qianlong Xuan paper with the initial contact angle being the smallest. It favors the absorption of the liquid with the largest contact area. In turn, a slow decrease in the contact angles results from slow absorption by the bulk paper[16]. By modeling voids or “pores” formed between fibers as a series of circular non-connected, parallel capillaries, the rate at which a liquid moves through the capillary tubes is related to the driving force by Poiseuille’s law,

dv πrp4Δ = , (2) dt 8ηh

where r is the equivalent radius of the capillaries, η is the liquid viscosity, h is the distance within the tubes, and Δp is the effective Fig. 3. (a) FT-IR ATR spectra of the three paper samples. Inset: portion of the spectra pressure gradient. −1 in the range of 900–1200 cm . (b) Ratio of the integrated intensity of OH- When a liquid front comes in contact with the entrance of a tube, stretching vibration band at 3000–3650 cm−1 relative to the characteristic vibration band at 900–1200 cm−1 for the Qianlong, Bamboo and Jingpi Xuan paper samples. a concave meniscus is produced. The typical Laplace pressure exerted by the formation of a meniscus at the interface is proportional to γ/r with γ being the surface tension of the liquid. The order of r is Meanwhile, the pectin and wax in the plant fibers are respon- 10−5 m and so the pressure has the order of 103 Pa. The hydrostat- sible for the non-wetting behavior of water and these substances ic pressure between the top and bottom of the paper is in proportion are removed from the process of alkaline cooking used in the manual to the thickness of paper. The order of the thickness is 10−4 m and manufacturing. For Qianlong Xuan paper made by the sophisticat- therefore, the pressure is on the order of 1 Pa. The former is much ed methods, the residues may be few. As aforementioned, the stream more than the latter, so gravity can be neglected. in Jing County possibly affects the performance of the paper. There The driving force generated by the concave meniscus is de- may be a linkage between the minerals in the water and the groups scribed by: on the fiber surface resulting in the increased surface free energy 2γθcos of the fibers and decreased contact angle. Δp = , (3) Wettability is the initial process, followed by wicking through r the capillaries. When the liquid wets the fibers, it reaches the spaces where θ is the contact angle. between the fibers and the capillary flow is triggered. In oriental Combining Eqs. (2) and (3) leads to Eq. (4) (classical Washburn– brush painting, when the brush used with a round bristle tip con- Lucas equation[17]) as shown below: tacts the absorbent paper, some amounts of ink are transferred to the paper. The circumstance is similar to a drop deposited on paper dv πγcos θr 3 = . (4) and so it is necessary to understand how a drop interacts with paper. dt 4ηh

3.4. Transverse wicking According to Eq. (4), it can be concluded that a small contact angle and a large effective radius are beneficial to transverse wicking. A drop with a small contact angle accelerates absorption[15].A Compared to Jingpi, which has more short rice fibers as fillers poorly wetting liquid cannot easily penetrate the complex inter- marked as a triangle in Fig. 5(a), Qianlong Xuan paper contains more [4] nal geometry of a porous system. It is well known that the drop long bark fibers, which constitutes the backbone of the paper . Short exhibits a dynamic contact angle on porous paper. In order to un- fibers can more efficiently pack in a dense network thereby reduc- derstand the process clearly, the contact angles as a function of time ing the permeability[18]. Additionally, there are chemicals as fillers on the three paper are shown in Fig. 4. The measurements are per- marked as a rectangle on Bamboo paper in Fig. 5(a). To a certain 186 S. Wu et al. / Journal of Materials Science & Technology 32 (2016) 182–188

Fig. 5. (a) SEM top-images and histogram of distribution of the fiber widths determined by SEM, (b) cross-sectional view of the fiber arrangement, and (c) the fiber surface topography of Qianlong Xuan paper (A), Bamboo paper (B), and Jingpi (C), respectively. extent, there are more voids or pores in Qianlong Xuan paper. There- brush strokes, and variations in the ink dispersion. Longitudinal fore, there is no doubt that the effective radius of Qianlong Xuan wicking plays a crucial role in the successful expression. paper is largest. Moreover, the permeability varies exponentially with The liquid ink is a diluted mixture consisting of water, soot, and the porosity over a long range of porosity[19]. This explains the dis- glue[20]. Soot is composed of spherical primary carbon particles about tinct transverse wicking, too. 10 to 150 nm in size[21]. Because of the water pressure and capillary force, water flows slowly carrying pigments with it through the fibers while 3.5. Longitudinal wicking pigment diffusion itself can be neglected[3]. Thus, it is essential to fathom water flow, especially that associated with in-plane wicking. Xuan paper is thin, textured, and absorbent and supports all the Fibers morph into flat and flexible ribbons during sheet forma- nuance of nature’s color as expressed by the shade of black, delicate tion. As shown in Fig. 5(a), the fibers are distributed relatively evenly S. Wu et al. / Journal of Materials Science & Technology 32 (2016) 182–188 187

Fig. 6. AFM images: (a) Wingceltis bark fiber, (b,c) fibers composing Jingpi and Bamboo papers, (d) average root-mean-square roughness of the three fibers. in Qianlong Xuan paper, while the fibers overlap densely some- tribution of the fibers is relatively localized, thus enabling the fibers where but the overlapping areas are far from each other as marked to interweave to form an even surface, too. Moreover, as shown in ellipses and arrows in Bamboo and Jingpi papers. The homoge- Fig. 5(b), the fiber web is much denser in Qianlong Xuan paper. The neous fiber distribution may be related to natural paper additives densities are 463, 356, and 429 kg/m3 for Qianlong, Bamboo, and such as kiwi fruit juice, which, as a dispersing agent, separates the Jingpi Xuan paper, respectively. When the liquid meniscus moves fibers in the suspension where flocculation of fibers takes place in the wedge-shaped channels with a small depth formed between readily due to the various colloidal, electrostatic and mechanical at- overlapping fibers, the advancing front will be smoother due to the tractive forces. When the gap formed between the fibers becomes crossover length from nonlocal to local dynamic scale with the sep- wider, the meniscus radius increases, making the liquid progres- aration d as d1/2 for the spontaneous imbibiting fronts[25]. The cross- sion more difficult. Thus, the ink flows correspondingly freely section of Bamboo paper is sparse corresponding to an irregular edge. resulting in a large spreading area and a clear edge in Qianlong Xuan There are many grooves along the central axis of wingceltis bark paper. fibers on the original smooth surface after natural drying[4].Ac- A smooth edge is related to the close global interconnectivity cording to the images of fibers at high magnification in Fig. 5(c), as well as good wettability. The greater connectivity of the inter- the surface of the bark fibers shows grooves while the Bamboo fiber faces in 3D leads to smooth advancing fronts below a critical contact surface is relatively smooth. These grooves, as open capillaries, form angle. In addition, for a large contact angle, only parts of the pores potential flow paths with increasing surface roughness. In terms of are filled thereby resulting in a fractal-like wetting front[22]. Mean- micro-fluid dynamics, when a liquid flows in open V-shaped cap- while, as the invading fluid becomes more wetting, cooperative illary grooves, the spreading length, z, of the liquid follows the invasion mechanisms may lead to a transition from fractal to compact following relationship: growth, leading to smaller roughness of the interface[23]. For Qianlong 2 Xuan paper, the good wettability has been verified. Hence, it should zK= ()αθ,,[] γ h0 η t (5) also have the best interconnection. Concerning the interconnectivity, Hasuike et al. have demon- where K(α, θ) is a geometric term containing the groove angle α strated that a vast interconnected network is formed by the massive and contact angle θ independent of the groove height, γ is the liquid [24] density of fiber overlapping . The extent of fibers overlapping is surface tension, ho is the groove height, and η is the liquid viscos- assessed by SEM. The average statistical results of fibers overlap- ity, implying that a deeper groove helps the flow[26]. ping per millimeter are 77, 52 and 40, respectively, for Qianlong, AFM is a useful supplement to SEM in characterizing surfaces. Bamboo and Jingpi Xuan paper. Most fiber overlapping in Qianlong The AFM images of the fibers in the paper samples are displayed Xuan paper matches expectation. Larger overlapping areas are related in Fig. 6(a–c). The surface roughness of the wingceltis bark fiber looks to more wider fibers. Thus, two hundred fibers are measured for the largest while the fiber surface of Bamboo paper is quite smooth. each paper and the bar graph is exhibited in Fig. 5(a). For Qianlong To describe the roughness more quantitatively, five random fibers Xuan paper, the wide fibers are dominant. Furthermore, the dis- were selected and measured from each kind of paper samples. The 188 S. Wu et al. / Journal of Materials Science & Technology 32 (2016) 182–188 average root-mean-square roughness values of the wingceltis bark as well as Red-Star Xuan Paper Limited Liability Company of China fibers and the other two fibers of Bamboo paper and Jingpi are cal- for kindly providing Qianlong Xuan paper and Jingpi. This work was culated to be 1055, 497, and 745 nm, respectively, as shown in jointly supported by the National Basic Research Programs of China Fig. 6(d). With respect to the plant fiber network, it follows Wenzel’s (No. 2011CB922102), the National Natural Science Foundation of relationship[27]: China (No. 11374141) and the City University of Hong Kong Stra- tegic Research Grant (SRG, No. 7004188). cosθθ* = r cos , (6) where θ* is the apparent contact angle, θ is the contact angle on the References flat surface and r is the ratio of the actual solid area over its pro- jected one. 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Lett. 20 (1988) 2045–2049. homogeneous fiber distribution related to the raw material and a [23] N. Martys, M. Cieplak, M.O. Robbins, Phys. Rev. Lett. 66 (1991) 1058–1061. [24] M. Hasuike, T. Kawasaki, K. Murakami, J. Pulp. Pap. Sci. 18 (1992) 114–120. dispersing agent, smaller distance between overlapping fibers re- [25] D. Geromichalos, F. Mugele, S. Herminghaus, Phys. Rev. Lett. 10 (2002) 104503. sulting from the denser fiber network, and the roughness of fiber [26] R.R. Rye, J.A. Mann, F.G. Yost, Langmuir 12 (1996) 555–565. surface concerned with sun bleaching make wicking strong and dis- [27] R.N. Wenzel, Ind. Eng. Chem. 28 (1936) 988–994. ordering in the short range increase; that is to say, natural materials Prof. Xinglong Wu is currently a Deputy Dean of School combined with ingenious traditional processing technique endow of Physics of Nanjing University. He received his Ph.D. Qianlong Xuan paper the unique performance. Compared to Qianlong degree in 1994 from the Department of Physics of Nanjing University. His research is concerned with the prepara- Xuan paper, Bamboo and Jingpi ones have relatively weak wetting tion, microstructures and electronic/phonon properties due to lower hydrogen bonding ration, more fillers, more non- of semiconducting nanostructured materials. He has co- uniform fiber arrangements, and smoother fiber surfaces, which authored over 280 scientific articles and filed 8 Chinese patents during the last 15 years. He has won 4 research- makes ink expression slightly weaker. The improved manufactur- related national awards from Jiangsu province of China. ing process will be of great benefit to the development of Xuan paper. He served as a member of the editorial board of Journal of Materials Science & Technology and other 3 internation- al academic journals. Acknowledgments

The authors thank Professor Fang Xiaozhuang from Academy of Fine Arts of Nanjing University for writing on three paper samples