Analytical Investigation Into Feather Decoration Technique of 17th-18th Century Chinese Royal Hanging Screen

Decoration with feather was a universal phenomenon in human history. Objects decorated with feathers were regarded as ne artworks and hence were enormously prized. In ancient China, dotting a surface with kingsher-feather blue was the most famous, complex and delicate feather decoration technique, called diancui. Although various ancient diancui artworks appear in many museums around the world and some researches have achieved signicant results on the history, technique and conservation of diancui, but some key historical details are still not clear. In this research, by the opportunity of restoration, an important collection of the Palace Museum - the “Feather Decoration Hanging Screen with Birds and Flowers Pattern” was rounded analyzed by various scientic technologies. This object is a Chinese royal artwork of Qing dynasty (17th-18th century), decorated with kingsher and several other bird’s feathers, and present the highest level of this period. As a typical and valuable case, the result provides important clues for solving unclear questions for related academic eld.

areas to rich the colors and patterns. What other feathers were used? Was the technique same with king sher feather?
Analytical investigation on typical ancient diancui objects could be the most effective way to answer these questions. But normally, existing diancui objects are rare and precious because they are fragile and hard to preserve. Lack of sample limited research in this eld. The Palace Museum China contains abundant diancui artworks of Ming and Qing dynasty. In this research, by the opportunity of restoration, an important collection of the Palace Museum -"Feather Decoration Hanging Screen with Birds and Flowers Pattern" was rounded analyzed by various scienti c technologies. This object is a royal artwork of Qing dynasty (17th-18th century), decorated with king sher and several other kinds of bird's feathers, and present the highest technique level of this period. As a typical and valuable case, the result provides important clues for solving unclear questions mentioned above.

The Hanging Screen
The hanging screen investigated in this study is a collection of the Palace Museum China, named as "Feather Decoration Hanging Screen with Birds and Flowers Pattern". It is considered that the hanging screen was made for the emperor in Qing Dynasty (17th-18th century). But the exact production date is unknown.
Normally, diancui technique was used to make small objects (for example jewelry) because of the rarity of the material and the di culty of the process. But this hanging screen is not only big (width 795mm and high 1130mm) but also have ingenious design and exquisite craft. As it reached the highest level of the royal diancui artworks in ancient China.
As shown in Fig. 1, the pattern of the screen is that two birds are standing on two stones with background of trees, owers and ground. There are 4 kinds of feathers used in the screen: the bird's body, leaves and owers were made of light blue feather; the stones and some parts of the birds were made of violet feather; the tree trunk was made of brown feather; the ground was made of dark irisated feather and eaten by insects seriously.

Samples
The most parts of the screen were in good condition. And only nondestructive analysis without sampling were acceptable. But a small leaf part dropped from the screen (Fig. 2) could be used for micro sampling before restored and pasted back. In addition, a small fragment from the ground area could be used for cross section analysis. Modern king sher feather was also used for comparing with the feather from the screen.

Experiments
Variety of microscopes were used for observing micromorphology: video microscope (LEICA DVM5000) with a cross cantilever for observing in situ; metallographic microscope (LEICA) with a spectrograph for observing the cross section and collecting the visible spectrum of the micro area of feather; biological microscope (Olympus) for analysis the paper base bers dyed by Herzberg reagent; SEM (FEI Quanta600) with EDS (EDAX Genesis) for elements imaging of cross section; FESEM (Tescan mira3) for observing the Nano coloration structure of king sher feather.

The Light Blue Area
The light blue feather was the most common used in diancui. Fortunately, the dropped leaf part from the screen is light blue, and could be overall analyzed. According to the damaged part ( Fig. 3 (a) and (c)) and ank side ( Fig. 3 (b)), there are 6 layers in this part as shown in Fig. 3 (d). The analytical investigation result of every layer was shown in Table 1.
According to the investigating on modern diancui craftsmen, a rough process of diancui is as follow. First, put feather back side up on a panel. Then brush glue on the back side of the feather. At last, separate the feather from the panel by knife as a feather sheet when the glue dried. This process can protect the feather bers to scatter and make it easier to cut to required shape. Then the feather sheets are glued on a support body. The analytical results of this screen t the rough process well, but more details were found. The following is the detailed analytical result and discuss: Layer 1: Layer 1 is the surface feather layer. It is obvious that this layer was spliced by small pieces of feather because the seams could be found through microscope (Fig. 3 (c)). There is a golden line decoration on Layer 1, which was proved by XRF. In order to identify whether the feather is from king sher, several methods were used to compare with the modern king sher feather. And the result showed that they matched well.
First, they were compared by stereoscopic microscope. As shown in Fig. 4, the color and size of these two feathers was consisitent. Both of the colors appears dense and varying shades of blue spots. The screen feather (40~50μm) is a litte smaller than the modern one (60~70μm). This difference may be caused by individual differences of king shers or growing in deifferent location of king sher body.
Second, the color of king sher feather is a kind of structural color which formed by interference, diffraction and scattering of light by Nano structural of feather [11]. This is why the color of diancui is constant. In ltration by liquid with high refractive index is a simple method of veri cation structural color [12]. As shown in Fig. 5 (a) and (b), some parts of the screen feather changed to transparent brown color and the visible spectrum redshifted (Fig.5 (c)) after in ltrated by isoamylol (refractive index = 1.4). When the isoamylol volatilized, the color was back to blue. This phenomenon showed that the feather has structural color, but not dyed. The result of FESEM supported this conclusion: the medulla of the feather form the screen Fig. 6 (a) has the similar Nano net structure with the modern feather Fig. 6 (b).
Layer 2: Normally, this layer was kind of glue that was painted on the back side of feathers to bond the feather bers to a feather sheet. So that cutting and pasting would be much easier. So normally this layer is called "back side glue layer". Micro-sample of this layer was tested by microscopic FTIR. The result shows that the glue material is protein and maybe animal gelatin, according to the bands of 1650 cm-1 (C=O stretching band), 1550 cm-1 (C-N-H bending band), 1450 cm-1 (CH bending band) and 3350 cm-1 (N-H stretching band) in the spectrum of Fig. 7 (a) [13].
According the Fig. 3, this layer is not only glue but also added black pigment. The black color can be seen through the gaps between feather bers. So, another function of this layer was that making the sensorial color of the diancui surface darker and the texture of feather bers clearer. The bands of 1350cm-1 and 1590cm-1 in the Raman spectrum (Fig. 8) are the D-band and G-band of carbon [14]. This shows that the black pigment of this layer is carbon black.
Layer 3 and Layer 6: The function of Layer 3 was bonding the feather sheet (layer1 + layer2) and support body (Layer4+Layer5+Layer6) together. The function of Layer 6 was bonding the diancui component on the screen. The FTIR spectrum ( Fig. 7 (b)) of layer 3 and layer 6 is consistent. The bands of 3310 cm-1 1647 cm-1 1545 cm-1 1448 cm-1 shows that the materials is protein and maybe animal gelatin [13].
Layer 4: This is a red layer on the top of the support body. Normally, it was call called "back side color layer". Its function was adjusting the sensorial effect of color and texture of the surface because the "back side glue layer" are often transparent and the color of this layer can be seen through the gaps between feather bers. In this case, even Layer 2 is already black, this layer was still painted red. The purpose may make the color of diancui surface look a little warmer. The XRF test result shows that the main elements in this layer are Fe, Al and Si. So the red pigment may be ochre. The FTIR result (Fig. 7 (c)) also supports this inference. The bands of 3695 cm-1, 3620 cm-1, 1036 cm-1, 910 cm-1 is the characteristic of Al2O and SiO2 from clay [13], which often accompany with ochre [15]. On the other hand, the bands of 3310 cm-1 1647 cm-1 1545 cm-1 1448 cm-1 shows that the materials could be gelatin [13].
Layer 5: Support body is the supporting structure of a diancui object and made by metal or paper. Silver and gold were soft and easy shaping. Therefore, commonly used for making metal support body. Paper support body was widely used in Qing dynasty for big jewels or furnishings, because it was much lighter than metal. The support body was rare studied before. In this research, the layer 5 is the main part of the support body and made by several layers of paper. In the FTIR spectrum (Fig. 7 (d)), the bands of 3335 (OH str) 1430 (CH2 def) 1370 (CH def) 1317 (OH def) 1160, 1105, 1054 (C-O str of COH/C-O-C) 898 (Ring semi-circle str) are consistent with cellulose of paper [16]. Fig. 9 is the microscope picture of paper bers. Observing by a biological microscope, the color of bers looks blue or brown after dyed by Herzberg reagent. The shape of the bers is straight with cuspate end. The parenchymatous cells, sclereids and duct could be found. These show that the paper is made of bamboo [17]. A stick is sandwiched in the paper layers as a skeleton to make the support body stronger. The material of this stick is copper according to the result of XRF.

The Violet Area
On this screen, the stone, beak and wings of the birds were made by violet king sher feather. Different with the light blue area, Fig. 10 shows that the back glue layer of violet feather was transparent, and the back side color layer was red. This design made the sensorial color of diancui surface brighter. An interesting discovery was that the feathers of bird beaks ( Fig. 10 (a)) was sparser than other parts ( Fig.   10 (b)). So the color of beak areas looks redder and close to rosy. Obviously, it's not an accident. This discovery means that the ancient craftsmen can change the gaps between feather bers to adjust the holistic color appearance. The XRF result shows that the main elements of the red layer are Fe, Al and Si, so the red pigment may be ochre. Further analysis did not carry out, because sampling was not allowed.

The Ground Area
The ground area had been damaged by pests. And layers under the feather can be seen in some cracked parts. As shown in Fig. 11, 4 layers could be found in the cracked area (a) and the cross-section image of a fragment sample (b).
Layer 1 was a kind of dark feather with irisation. The microstructure of the feather ber ( Fig. 12 (a)) was bamboo-like and similar with the peacock feather ( Fig. 12 (b)). The difference was that the feather of the screen was ater than the modern feather. It means that the peakcock feather on the screen may be scraped.
Layer 2 may be the back glue layer and bonding layer together. It was transparent. So the back side color layer under this layer could be seen. The appearance and FTIR spectrum of this layer were same with the Layer 3 and 6 of the light blue area. The material could be gelatin.
Layer 3 was the back side color layer. The element Ag can be found in this layer from the SEM-EDS mapping ( Fig. 13 (b)). So this layer should be a silver foil and for enhancing the shiny and irisated effect of the feather surface appearance. The feather was pasted on the silver foil by yellow transparant gelatin which made the foil look like gold. The technique may be a design to disguise as gold foil and save cost.
Layer 4 was used for stick the silver foil on support body. It is common that adding red pigments in the glue for bonding foils in China. SEM-EDS mapping (Fig. 13 (c-f)) shows that the main elements of this layer are Fe Al Si O. The FTIR spectrum and elements result are almost same with the layer 6 of the light blue area. So this layer could be a mixture of ochre and gelatin. Additional structure was found in the SEM picture ( Fig. 13 (a)) under this layer. They might be the paper ber from the support body. Fig. 14 (a) shows that the surface of the tree trunk area was made by a kind of brown down feather because the barbs are thin without hook and the barbules are thin and long. Further analysis for identi cation of species did not carry out, because sampling was not allowed.

The Tree Trunk Area
Different from other areas, A white thick layer under the feather could be found at the damaged position ( Fig. 14 (b)). The purpose of this layer was making a raised shape like real tree trunk. The white material was identi ed as CaCO3, according to the characteristic bands of 1440 cm-1 and 880 cm-1 of the FTIR spectrum (Fig. 15) [13]. The high signal of Ca element in XRF result was also support it.

Conclusions
Decoration with feather was a universal phenomenon in human history. In this academic subject, Chinese tradition is an inescapable part. But some key historical details are still not clear. The hanging screen, investigated in this paper, is a typical royal feather decoration artwork of 17 th -18 th century China. The research results provided important clues for understanding the complex ancient diancui techniques better and solving following unclear questions.
(1) Even only two kinds of king sher feathers were used, how did the ancient craftsmen adjust the color and texture of the nishing surface to reach a rich and vivid decorative effect?
Using back side color was one of the main ways to adjust the sensorial color and texture of the diancui objects. In this hanging screen, double back side color layer (black and red) was used to make the light blue feather looks darker and warmer and the texture clearer. Red back side color layer was used to make the violate feather looks brighter. Adjusting gaps between feather bers was another main way. The feather of bird beaks of the screen was sparser than other parts. So the color of beak looks redder and close to rosy.
(2) What materials and technique were used in the support and adhesive parts of diancui objects which are under the feather layer and hard to be directly observed?
According to the investigation on modern diancui craftsmen, there were normally two adhesive layers: back side glue layer and bonding layer. The function of the back side glue layer was bonding feather bers together to a feather sheet. So that cutting and pasting small feathers would be much easier. The bonding layer was for bonding the feather sheet and support body together. The analyzing results of the screen supported this process well. Additionally, for the light blue feather, carbon black pigment was added in the back side glue layer and also used to adjust color and texture beside the back side color layer.
The support body of this screen was made of multi-layers of bamboo paper. Gelatin was used for bonding paper together. A copper stick was sandwiched in the paper layers to strengthen the body. The purpose of this design might be weight reduction for large diancui objects.
(3) What other feathers were used along with king sher feather? Were their techniques same with king sher feather?
Peacock feather was used in the ground area of the screen. The main structure of this area is similar with the diancui area. The difference is mainly on the back side color layer. The material of back side color layer is silver foil but not pigment, for enhancing the shiny and irisated effect of the feather surface appearance. Interestingly, the feather was pasted on the silver foil by yellow transparant gelatin which made the foil look like gold. This technique may be a design to disguise as gold foil for saving cost.
A kind of brown down feather was used in the trunk area of the screen. The layer under feather is different from other area. A raised shape was made by thick CaCO3 in this layer to imitate the real tree trunk.

Declarations
Availability of data and materials The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request. The main part of the support body.

Skeleton Brown Copper
Be sandwiched in the paper layers to make the support body stronger.   Table 1.
Page 13/18 Figure 4 Comparing the feather from the screen (a) with the modern king sher feather (b).

Figure 5
The color change of the feather before and after in ltrated by isoamylol. (a) before (b) after (c) the visible spectrum Figure 7 The FTIR spectra of Layer2 (a), layer 3 and 6 (b), Layer4 (c), Layer 5 (d).

Figure 8
The Raman spectrum of Layer 2.

Figure 9
The biological microscope picture of paper materials in Layer 5. The bers, parenchymatous cells, sclereids (a) and duct (b) could be found.

Figure 10
The microscopic image of the bird beak part (a) and other part (b).

Figure 11
Four layers were found in cracked area (a) and cross section of a fragment (b) Figure 12 The microstructure of the feather of the ground area (a) and modern peacock(b).

Figure 13
The SEM-EDS elements mapping of Layer3 and 4.

Figure 14
Brown down feather on the surface (a) and white thick layer under the feather (b) Figure 15 FTIR spectrum of the white layer.