3.1 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 flank 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 fibers 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 fit 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 kingfisher, several methods were used to compare with the modern kingfisher 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 kingfishers or growing in deifferent location of kingfisher body.
Second, the color of kingfisher 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. Infiltration by liquid with high refractive index is a simple method of verification 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 infiltrated 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 fibers 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 fibers. So, another function of this layer was that making the sensorial color of the diancui surface darker and the texture of feather fibers 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 fibers. 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 fibers. Observing by a biological microscope, the color of fibers looks blue or brown after dyed by Herzberg reagent. The shape of the fibers 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.
3.2 The Violet Area
On this screen, the stone, beak and wings of the birds were made by violet kingfisher 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 fibers 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.
3.3 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 fiber (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 flater 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 fiber from the support body.
3.4 The Tree Trunk Area
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 identification of species did not carry out, because sampling was not allowed.
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 identified 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.