The Historical Information of the Decorative Polychrome Painting in the Hall of Mental Cultivation Complex, Forbidden City

This paper analyses the decorative polychrome painting of architectural members (caihua) that has survived in the Hall of Mental Cultivation (Yangxindian) in the Forbidden City, Beijing. Beginning with the Yongzheng emperor, the Hall of Mental Cultivation was the residence and centre of daily governance for Chinese emperors. Combining information gained through on-site surveys and scaled drawings executed during a recent conservation project with evidence from historical records and other sources, this study finds that the remaining decorative polychrome painting can be dated to four different historical phases: the reign of the Jiajing emperor; the late Ming and early Qing dynasties; the reign of the Qianlong emperor; and the late Qing Dynasty and beginning of the Republic of China. It reveals that the designs of decorative polychrome painting on architectural members are closely related to changes in the functions of the buildings and imperial use. As part of an investigative conservation project, the study aims to provide a reliable basis for the conservation and repair work in the next step.


Introduction
The Hall of Mental Cultivation complex is situated to the west of the courtyard of Palace of Heavenly Purity (Qianqinggong) and to the south of the Six Western Palaces in the Forbidden City, Beijing. The major buildings in that complex were originally constructed in the 16 th century during the reign of the Jiajing emperor (r. 1521-1566) of the Ming Dynasty. The Kangxi emperor (r. 1661-1722) of the early Qing Dynasty assigned it as the Workshop of the Inner Court. After the Yongzheng emperor (r. 1723-1735) succeeded the throne, he used the hall as his residence and centre for daily governance. From his reign until the abdication of the Xuantong emperor (r. 1909-1912), eight emperors used the hall as their palace for living and administration. As the political core of the Qing Dynasty, the Hall of Mental Cultivation was the scene of major historical events in domestic and foreign affairs, the death of emperors, and the changing hands of power ( Figure 1).
The primary architecture in this complex is the 工shaped Hall of Mental Cultivation at the centre of the courtyard. The plan takes the shape of the Chinese character gong 工 , with a front hall for administration and rear hall for residence. The bays in the centre of the front hall were used for the emperor to handle state affairs. The western warmth chamber (nuange) of the front hall was where the emperor read memorials to the throne and held confidential conversations with ministers. The Hall of Three Rarities (Sanxitang), the study of the Qianlong emperor, was set up in this room together with the place for the emperor to make offerings to the Buddha and relax. The eastern warmth chamber was where Empress Dowagers Cixi and Ci'an attended to state affairs behind a screen during the late Qing Dynasty (Figure 2).
The eastern side hall of the Hall of Mental Cultivation was a Buddhist prayer hall; the western side hall was for the consecration of tablets of deceased emperors. The rear hall was the residence of the emperor, with five subsidiary rooms in each of the two wings. The rooms in the east were used as the temporary residence of the empress; the rooms in the west were used as the residence of the highest-ranking imperial concubines. Around 10 bays of the surrounding buildings were set adjacent to the east and west of the main halls; they had small rooms, simple furnishings, and were used as the temporary residences of lower-ranking concubines. Still smaller buildings in front of the Gate of Mental Cultivation (Yangxinmen) were used by the eunuchs on duty who served the emperor (Figure 3).
At the end of 2015, the Palace Museum launched the 'Research-oriented Conservation Project for the Architectural Complex of the Hall of Mental Cultivation' . One of the primary tasks of this project is to assess and preserve the hall as a whole, with the decorative polychrome painting of architectural members (caihua) as an integrated part. This paper analyses the changes that took place with the decorative polychrome painting from the 14 th to early 20 th centuries in chronological order. The study detects the changes from various aspects, including review of historical documents, on-site investigation of existing buildings, study of the functions and their owners, and technological tests.

Reign of the Jiajing Emperor in Middle Ming Dynasty
The earliest date for the construction of the Hall of Mental Cultivation complex is significant when assessing the value of its architecture. According to volume 201 of Ming Shizong Shilu (Chronicle of Emperor Shizong of the Ming), the Hall of Mental Cultivation was completed in the sixth month of the 16 th year of the Jiajing emperor's reign (1537). However, the historical record does not clearly indicate whether this was a new construction. On-site investigations have revealed that most of the bricks were made in 1535; the timber used for the frame of the main hall is mainly nanmu (Phoebe zhennan S. Lee) 1 ; and the timber members show typical features of the Ming Dynasty. All these findings strongly support the complex having been at least extensively reconstructed and expanded during the reign of the Jiajing emperor. This dating is significant when studying changes in the layout of the Forbidden City in the middle and late Ming Dynasty.
There is no record of the function of the Hall of Mental Cultivation at the time of its original construction. A detailed study of this topic by Xieping Li suggests that as a subsidiary hall for the emperor in the Inner Court, the complex served as a religious area, the imperial kitchen, and a living area in different historical periods (Li 2016).

Central Bay of the Main Hall, and the Eastern and Western Warmth Chambers
The treatment of the ceiling and wooden materials used in this area indicates that the central bay of the main hall and the eastern and western warmth chambers date back to the Ming Dynasty. For example, the douba-zaojing (domed coffered ceiling with a curled-up dragon and mixed golden decoration) in the central bay of the main hall is believed to be a significant hallmark of architecture under the reign of the Jiajing emperor of the Ming Dynasty (Li 2016). In addition, the wood used in the frame of the main hall has been identified as being mainly nanmu 2 ;  that timber was also employed in the ridge of the central bay of the main hall as well as for components coated with decorative polychrome painting in the ceilings of the eastern and western warmth chambers. Features of the members in the wooden frame also conform with practice during the Ming Dynasty 3 . With regard to the decorative polychrome painting on the architectural members of the main hall, the blackinked, gilded xuanzi with a blank middle portion 4 , the baofu (frame of the caihua in the middle of a beam) with red inking, and the coloured cloud pattern on a golden ground painted on members of the ridge are believed to be original and to date from the Ming Dynasty (Figure 4) 5 . The craftwork on the three members of the ridge shows that they were directly painted onto the wooden surface, rather than onto a plaster base (dizhang). Both blue-green and green were shaded in the style of shinianyu 6 . Most of the pigments appear stable, which implies that they could be mineral pigments made from azurite, malachite, and cinnabar. Optical microscopic analysis of pigment samples confirmed that inference: most of the pigments were mineral, with only a few parts containing vegetable pigments (Figure 5) 7 . Two kinds of blue-green were used: azurite blue-green and indigo, on the bottom and sides of the tie beam (fang) of the ridge. Microscopic analysis of sections determined that there is no other layer of painting; thus, the paintings would appear to be original. Furthermore, the pigment layers indicate that the light colours were painted first: heiyanzi (black ash) used for hecao 8 is found in the ground layer, and darker colours were successively overlaid upon it. That is the reverse of the practice during the Qing Dynasty, which began with colours and ended with white. Therefore, it is confirmed that the decorative polychrome painting on the members of the ridge were painted during the reign of the Jiajing emperor.

Hall of Joyful Swallows (Yanxitang)
The Hall of Joyful Swallows is the western subsidiary room of the rear hall of the Hall of Mental Cultivation 9 . The building was probably constructed during the reign of the Kangxi emperor in the Qing Dynasty. During the reign of the Yongzheng emperor, the Hall of Joyful Swallows became the temporary accommodation for high-ranking concubines when they served the emperor at night. It was also a temporary residence for Empress Dowager Cixi when she attended to state affairs behind a screen during the reign of the Tongzhi (r. 1862Tongzhi (r. -1874 and Guangxu emperors (r. 1875Guangxu emperors (r. -1908.    Although the Hall underwent repair many times from the time of the Ming to the Qing Dynasty, the original wooden frame still largely exists 10, 11 . Although the pigments 12 of the decorative polychrome painting at the front eave have been largely covered by pasting paper during the decorative works conducted through history, the contours of the patterns are still recognisable. For example, the painting at the ends of the horizontal architrave linking (e'fang) are in the shape of one whole and two half ruyitou patterns with three curves. The ends of the middle portion (fangxintou) feature double concave lines ; the ends of the timber members are painted only with secondary head hoop (gutou). Moreover, the painting was painted directly onto the horizontal architrave without a plaster base ( Figure 6). Both blue-green and green were shaded in the style of shinianyu, which is typical of craftsmanship in the early and middle Ming Dynasty. The stylistic features are similar to those on the tie beam of the ridge of the main hall and under the front eave of the 13 th bay from the south of the western surrounding building (Table 1).
Judging from the characteristics of the timber frame and the decorative polychrome painting on architectural members of the Hall of Joyful Swallows, it is clear that the interior painting on the horizontal architrave of the front eave is in the official style of the Ming Dynasty, with the patterns and styling inheriting the practice of the early Ming Dynasty; thus, the wooden frame should have been finished by 1537.   The lower layer is flat and pasted by blank white paper The upper layer is in the style of wuding and pasted by a soft ceiling of lotus-and-watergrass pattern

Late Ming Dynasty and Early Qing Dynasty
From the late Ming Dynasty, the Hall of Mental Cultivation was used for both residential and administrative purposes. From 1690 to 1708, under the reign of the Kangxi emperor, the Department of Imperial Household Construction (Zaobanchu), together with its workshop, was established there. The Hall formally became used for both residence and administration during the reign of the Yongzheng emperor. Interior decorative polychrome painting on girders and beams of the eastern and western warmth chambers of the main hall, eastern and western side halls, eastern and western surrounding buildings, the Hall of Joyful Swallows, and the gong-shaped gallery were partly altered during that period. The alterations reflect changes to the interior decorations of the Hall of Mental Cultivation conducted in the early Qing Dynasty; they are significant to studies of changes made to the architectural layout of the Forbidden City in the early Qing Dynasty.

Eastern and Western Warmth Chambers of Main Hall
The ceilings of the eastern and western warmth chambers are in the form of two layers of an unpainted wooden lattice (baitangbizi), which is a rare feature in the Forbidden City. The lower layer is a flat ceiling pasted with paper, which joins the interior top of the horizontal architrave to hold bracket-sets (pingbanfang). The upper layer is in the style of wuding (fixed on five sides) 13 ; it joins the beams attached to the ceiling and is pasted using the craft of 'soft ceiling' 14 ( Figure 7). Investigation during a conservation project revealed that only fragments of the ceiling survive; and it is inferred from the remaining features of the ceiling that its decorative polychrome painting would have been in a lotus-and-watergrass pattern ( Figure 8). Accordingly, it is necessary to determine when the ceilings were installed and what was the terminus ante quem of the decorative polychrome painting on the ceilings and wooden frame members. As evident in Cheng Zhang's Diary (1690) 15 , the Department of Imperial Household Construction was established in the Hall of Mental Cultivation no later than 1690; the walls and ceilings of the warmth chambers were already pasted with white paper. This means that the terminus post quem of the lower layer of ceilings would be 1690 and the terminus ante quem of the upper layer and decorative polychrome painting on the wooden frame members should be the same year ( Figure 9, Figure 10). Compared with that on the ridge purlin of the main hall, the painting here would have been executed after the reign of the Jiajing emperor of the Ming Dynasty. Thus, the decorative polychrome painting of the eastern and western warmth chambers of main hall should date from the late Ming and early Qing dynasties.

Eastern and Western Side Halls
There is no record of major repairs to the eastern and western side halls of the Hall of Mental Cultivation following their construction. Thus, the wooden frames of the Ming Dynasty are largely conserved, with the characteristics of the wooden frame members generally match the practice during the Ming Dynasty 16 . The interiors of the two side halls feature whitewashed walls pasted with white paper. However, an on-site investigation found that unpainted wooden lattices are installed behind the paper on the gable walls and rear eave wall. The wooden frame members above the lattices are covered by black-inked, gilded xuanzi-caihua, which is similar to that found in the ceilings of the eastern and western warmth chambers ( Figure 11a, Figure 11b, Figure 12). The rear eave walls and gable walls under the beams and girders are earthen walls covered with gold. The connecting ceiling beam at the rear eave purlin, which joins the fivepurlin beam, is painted green. Traces of green connecting ceiling beam are also left at the bottom of the five-purlin beam at the north gable wall of the northern subsequent bay and top of the intermediate purlin of the front eave of the eastern side hall. All these evidences imply that in the side halls, there were wooden frames under the ceilings covered by decorative polychrome painting; the earthen walls were covered with gold, decorated with wide granular-green edges and black-and-white decorative lines ( Figure 11c). This style of interior decoration dates from the late Ming and early Qing dynasties.

Hall of Joyful Swallows
Decorative polychrome painting of the Ming Dynasty remain inside the front eave of the central bay, adjacent bays, and the eastern subsequent bay of the Hall of Joyful Swallows. Further, traces of stick-shaped components used for support are evident in the following places: above the unpainted wooden lattice ceiling; on the joist of dou (yadoufang) of the front eave; and in the middle part of the four-purlin beam inside the western subsequent bay. Bracket sets and interconnecting boards under the top column joist (zhengxinfang) were replaced by a wooden board. These findings signify that there was formerly a latticed ceiling; the wooden frame under the ceiling was covered by decorative polychrome painting, and the gable walls of the subsequent bays were earthen walls covered by gold ( Figure 13a, Figure 13b). Jambs covered with red oil paint and green connecting ceiling ring beams are found under the four-purlin beams below the pasting paper. This means that the eave columns were originally covered with red oil paint, and there used to be a ceiling. That is most probably the interior decoration style before the 7 th year of Yongzheng (1729). The ceiling beams are painted with yawumo-caihua, which indicate a relatively low rank. That is not in accordance with the type of painting used for the residences of the emperor or concubines. Thus, they may not have been painted before the reign of the Yongzheng emperor.
The Hall became the residence of concubines after the 7 th year of Yongzheng (1729) 17 . So a new ceiling was installed at the level of the four-purlin beams and front eave; the paper pasting work was done again. The decorative polychrome painting on the wooden frame of the   (Table 2).

Eastern and Western Surrounding Buildings
According to Huangcheng gongcheng yashu tu (Painting of the Governmental Offices in the Imperial Palace of the Imperial City) ( Figure 14) 19 of 1679 and Qianlong jingcheng tu (Painting of the Capital City under the Reign of the Qianlong Emperor) ( Figure 15) 20 of 1750, these two buildings before the early Qing Dynasty were independent; they had 12 bays on both the eastern and western sides. The rear hall and its two subsidiary rooms were also independent; these five buildings were not linked to one another. By 1750, the subsidiary rooms became connected to the rear hall; the surrounding buildings 21 became connected to the three buildings of the rear hall with colonnades of 18 bays on both sides 22 . Two more bays were added to the northern ends of the surrounding buildings so that they could align with the rear eave walls of the subsidiary rooms. The surrounding buildings originally lacked ceilings: all the wooden frame members were painted, and the rafters were painted green. The current investigation determined that part of the rear eave walls behind the interior pasting paper of the western surrounding building were earthen walls covered with gold. Sill frames occur under the pasting paper at the level of the five-purlin beams. The interior columns and sill frames are covered by red oil paint; partition boards pasted with paper were added in a later period. The wooden frame features of these two buildings match the practice of the Ming Dynasty. For example, the craft of zengjian was used for the tenons at the joints between the horizontal architrave and the columns. Some of the bottom part of the blocks in the bracket sets used at the lowest purlins within the eaves are obviously curved; baffles (tuodangban) covered by red oil paint are employed between the three-purlin and five-purlin beams.
It may be inferred from historical records 23 that the eight bays in the north of the eastern and western surrounding buildings became residences for concubines in   14 15 the 7 th year of Yongzheng (1729). Unpainted wooden lattices pasted with paper were installed during the accompanying changes. All the remaining decorative polychrome paintings on the wooden frames of the surrounding buildings are xuanzi-caihua in five elegant colours; the middle portion has a '-'-shaped pattern. It shares the features of the painting in the eastern and western large buildings of the Gate of Divine Prowess (Shenwumen) and Imperial Tea House in the Forbidden City, which were painted in the late Ming and early Qing dynasties; thus, it should have been finished before the reign of the Yongzheng emperor (before 1723) ( Figure 16).

Decorative Polychrome Painting during the Reign of the Qianlong Emperor
In the middle Qing Dynasty, during the reign of the Qianlong emperor, the eastern warmth chamber of the Hall of Mental Cultivation was used as a residence and the daily administrative centre of the emperor. The Changchun Study, Xianlou Fotang (Buddhist prayer room with building models for celestial beings), Hall of Three Rarities, and other zones having different functions were set up in the western warmth chamber. Part of the decorative polychrome painting inside the central bay of the main hall were changed during this period, reflecting the history of changes to the interior decorations of the Hall of Mental Cultivation during the middle Qing Dynasty. Thus, the painting is significant to studies of the development of the architectural layout of the Forbidden City at that time.
According to on-site investigations, the decorative polychrome painting on the horizontal wooden frame members below the domed coffered ceiling and the ceiling of the central bay are in the type of dragon hexi with hooped gutou (Figure 17a, Figure 17b). Judging from the characteristics of the patterns, the craftsmanship, historical layers 24 , period when hooped gutou 25    painting is original and dates from the Qianlong period. The green pigments at the bottom layer possibly date from the same period as the architrave at the rear eave of the Buddhist prayer room and the painting on the edge of the earthen wall covered by gold at the rear eave of the central bay; both those features were decorations under the reign of the Kangxi emperor, when the Hall of Mental Cultivation was used as the office of the Department of Imperial Household Construction. A historical document from the 12 th year of Tongzhi (1873) records that the decorative polychrome painting on the wooden frame and the domed coffered ceiling in the main hall were renovated 27 . The top layer of pigments does in fact appear like the ultramarine and Paris green of the late Qing Dynasty. Optical microscopic analysis of sample sections has confirmed that there are three layers of decorative polychrome painting in the east and west axes of the central bay. The bottom layer is relatively thin, which implies that it could have been painted at the same time as the architrave at the rear eave of the Buddhist prayer room. Moreover, the test report confirmed that the pigments of the top layer of the painting are atacamite and Paris green; the blue-green and green pigment of the original painting are azurite, malachite, and atacamite. Therefore, it may be concluded that the decorative polychrome painting on the interior wooden frame of the main hall were renovated in 1873 based on the original patterns and colours of the Qianlong period.
In addition to the above findings, on-site investigation has revealed that all the major lines of the decorative polychrome painting on the horizontal wooden frame members are straight; that feature is different from the curved edge lines of the hexi-caihua in the Palace of Abstinence (Zhaigong) under the reign of the Yongzheng emperor. Straight edge lines with shadings outside the edges are characteristic of the practice that began in the middle and late Qianlong period. The zhaotou of the architraves of the east and west axes of the central bay of the main hall are painted with rising dragons, partly gilded on a bluegreen ground, and descending dragons, partly gilded on a green ground. The zhaotou of the architraves of the front and rear eaves are painted with descending dragons, partly gilded on a blue-green ground, and rising dragons, partly gilded on a green ground. The bodies of the dragons feature scales and a belly. That is different from the practice of the late Qing Dynasty, which depicted rising dragons on a blue-green ground and descending dragons on a green ground on zhaotou with the dragons' bodies featured solely the belly pattern. Hence, it may be concluded that the decorative polychrome painting on the wooden frame of the central bay matches the characteristics of the middle Qing Dynasty. The test reports of pigments and craftsmanship confirm that the pigments and craftsmanship of the toplayer painting date from the period of Tongzhi. During the investigation, multiple layers of renovations were found in the douba-zaojing, which had a curledup dragon and the ceiling of the central bay, which was

18
painted with rising dragons and descending dragons. The base of the ceiling was found to have a plaster ground made of linen cloth; silken cloth was mounted on multiple layers of paper pasted onto the linen, and patterns of rising and descending dragons were painted on the silken cloth. Further analysis of the painting revealed further indications of the period of execution. First, the bluegreen and green grounds within the yuanguzi (circle at the centre of a painted ceiling board) and fangguzi (square outside the yuanguzi) in the latticed ceiling had been renovated during the Tongzhi period; the pigments used were ultramarine and Paris green. Clearly, the wheel and swallow tail patterns (gulu-yanwei) on the bars of the ceiling were added at a later period ( Figure 18). Second, dragon and phoenix patterns in the douba-zaojing were all painted using the technique of saojin (golden powder applied on a special kind of glue) ( Figure 19). Optical microscopic analysis of the sample sections revealed that there were three layers of gold foil. They were probably applied by covering pink gold with tung oil, which matches the Record of Reimbursement by officials of the Imperial Household Department 28 . Traces of two to three layers of renovation were found at the blue-green and green grounds of the corners of the domed coffered ceiling; they are decorated with carved phoenixes. Optical microscopic analysis of sample sections revealed that the pigments used in the blue-green grounds are ultramarine, azurite, and malachite from, respectively, the top to bottom layers; those in the green grounds are two layers of green pigments. With regard to the corner tie beams, three layers of renovation are found; the pigments used from the top to bottom layers are, respectively, Paris green, ultramarine, and malachite. All this evidence confirms the historical documentation of 1873, which states, 'Exterior and interior decorative polychrome painting as well as the buharhut caps (pilumao) and the ceilings inside the Hall of Mental Cultivation were renovated based on old painting. '

Decorative Polychrome Painting in Late Qing Dynasty
During the late Qing Dynasty in the periods of Daoguang (1821-1850), Tongzhi (1862-1874), and Guangxu (1875-1908, Empress Dowager Cixi twice attended to state affairs behind a screen. During that time, Empress Dowager Ci'an lived in the Hall of Manifest Compliance (Tishuntang), Empress Dowager Cixi resided in the Hall of Joyful Swallows, and the eastern warmth chamber of the Hall of Mental Cultivation was where they attended to state affairs. At that time, the Hall of Mental Cultivation complex was the scene of significant turning points in the political history of the Qing, such as the inheritance of imperial power in the 13 th year of Tongzhi (1874) and the shift in the core of power in the 15 th year of Guangxu (1889). Interior fixtures in the complex were also changed, and the exterior decorative polychrome painting were repainted. These changes reflected the evolution of the decorations in the Hall of Mental Cultivation in the late Qing Dynasty; they are significant to the studies of the development of architectural layouts of the Forbidden City during that period.

Hierarchical Order of the Decorative Polychrome Painting at the Exterior Eave of the Hall of Mental Cultivation
According to a record from 1873 29 , the decorative polychrome painting on the interior eave, exterior eave and small projecting portico (baosha) of the Hall of Mental  Cultivation were renovated at that time based on the original painting. The lower frames of the surrounding buildings of the hallway and offices were also repainted that year. However, comparative analysis of the current situation, the pattern of colours, the techniques used, characteristics of patterns and layers of renovations of all the exterior decorative polychrome painting of all the buildings in the Hall of Mental Cultivation Complex reveals that the painting of the top layer matches the characteristics of the late Qing Dynasty; they were thus most probably painted then (Figure 20a, Figure 20b). There is no record of renovation of this part of the painting after the period of Tongzhi; so based on the bottom layer of the painting painted during the reign of the Qianlong emperor, it may be inferred that these exterior paintings were renovated in 1873. Judging from the current situation of the decorative polychrome painting in the Hall of Mental Cultivation complex, they were designed as a whole. They have strict ranks and are harmoniously coordinated, so as to serve the etiquette of the imperial household ( Figure 21).
The four ranks of the painting are as follows: dragon hexi; dragon-and-phoenix hexi; golden-inked dragonand-phoenix pattern; and black-inked minor golden xuanzi, with a middle portion featuring a dragon brocade pattern. They are used in accordance with the ranks and functions of the buildings. The highest-ranked buildings were where the emperor conducted state business and the Buddhist prayer room; the second-highest ranked was the residence of the emperor; the third was the temporary residence for the empress when she attended upon the emperor; that was followed by the residence for high-ranking concubines; that was further followed by the residences for the other concubines; temporary residences for imperial consorts of even lower ranks had lowly ranked layouts and decorations to match their status (Table 3).

Decorative Polychrome Painting at the Exterior Eaves of the Hall of Joyful Swallows, Hall of Manifest Compliance, Eastern and Western Surrounding Buildings and Other Buildings
The composite decorative polychrome painting with a middle portion of the golden-inked dragon-and-phoenix pattern on the exteriors of the Hall of Joyful Swallows, Hall of Manifest Compliance, and eastern and western surrounding buildings were painted during the Tongzhi period (1862-1874). They are rich in characteristics of the late Qing style and reflect the style of decoration during the period when Empress Dowager Cixi dealt with state affairs behind a screen; there was strict attention to ranks and orders (Figure 22a-22d   not belong to any of the five categories of official decorative polychrome painting under the Qing; it is a distinctive feature of the decorative polychrome painting system of the Forbidden City, and it renders this kind of painting rich in historical value and research significance. According to investigations of the remains of the exterior decorative polychrome painting of the Hall of Joyful Swallows, Hall of Manifest Compliance (except for the outer side of the eave-lifting beams [qingyanfang]), and eastern and western surrounding buildings, there are two kinds of framing compositions for the major lines of the composite golden-inked decorative polychrome painting. The first is for purlin beams (linfang; those above and below the eave-lifting purlins), on which the framing composition of xuanzi-and Su-style caihua is based. The second is for the upper and lower tie beams at the eave-lifting area 30 , on which the framing composition of xuanzi-and hexi-caihua is based. The patterns employed are dragons, phoenixes, and passion flowers. The dragonand-phoenix pattern is used only in high-rank Su-style caihua. Sunflowers and kuilong patterns painted at zhaotou usually appear in the early Qing hexi-caihua; zhaotou of sunflowers and glossy ganoderma patterns and the middle portion of the dragon-and-phoenix pattern occasionally appear in Su-style caihua; the zhaotou of xuanzicaihua are painted only with spiral flowers. Passion fruit ointment 31 was a medicine often used by emperors and empresses; the passion fruit pattern was frequently used as by them a decorative motif. With respect to the craft with gold foil, the major lines of painting are all embossed gilded double lines. Such patterns as those of the dragon and phoenix, passion fruit, and kuilong were partly gilded, and the hooped gutou were delineated with golden inking. In brief, these composite golden-inked painting combine the framing and layouts, pattern motifs, craftsmanship, and colour settings of hexi-, xuanzi-, and Su-style caihua.

Conclusion
The decorative polychrome painting on the architectural members of the Hall of Mental Cultivation complex reflects the history of construction and changes in functions of the buildings in the Ming and Qing dynasties. The decorative polychrome painting carry rich historical information and cultural connotations from different periods of history; the motifs used in those periods played a significant role in the design of the painting in that complex. The patterns used in the painting symbolise the ranks and identities of the feudal ruling class. In the middle Ming Dynasty, as the residence, imperial kitchen, and place for Taoist practices of the emperor, the wooden frame members at the ridge area of the central bay of the main hall were painted with black-inked golden xuanzicaihua of a high rank. In the late Ming and early Qing dynasties, the Hall of Mental Cultivation was a subsidiary hall for the emperor; it was used by the Department of Imperial Household Construction during the reign of the Kangxi emperor. At that time, the golden lotus-andwatergrass pattern and black-inked golden xuanzi-caihua was retained above the newly added ceilings of the eastern and western warmth chambers. Xuanzi-caihua in five elegant colours was used above the new ceilings of the eastern and western surrounding buildings. In the period of Yongzheng, the Hall of Mental Cultivation formally became a place for both residence and administration. The interior decorations were largely changed, especially during the reign of the Qianlong emperor. The rank of the painting on the wooden frame inside and outside the main hall was increased: dragon hexi-caihua appeared in the central bay; dragon-and-phoenix hexi-caihua appeared in the rear hall (emperor's residence) and gong-shaped gallery. During the periods of Tongzhi and Guangxu, Empress Dowager Cixi twice attended to state affairs behind a screen; patterns of dragon hexi, dragon-and-phoenix hexi, composite golden inking, and xuanzi were painted in different places of the exterior eave of the buildings belonging to the Hall of Mental Cultivation complex according to their function and rank in the hierarchy. The decorative polychrome painting from the middle Ming, late Ming and early Qing, middle Qing, and late Qing dynasties truthfully reflect the history of the architecture of the Forbidden City during those times, providing strong evidence for dating the buildings which is significant in studying the development of the architectural layout of the Forbidden City during those two dynasties.   (1) the fish-bellied four-purlin beams (yufuliang) within the structure, which is one of the characteristics of the wooden frames of the Ming Dynasty. This type of beam tapers from the middle to the ends, forming a gentle curve, which is similar in appearance to the shape of a fish's belly; it illustrates the legacy of crescent beam (yueliang) from the Song Dynasty with its exquisite craftsmanship and graceful shape; (2) the 'added shoulder' (zengjian) used for the tenons in the joints between the horizontal architrave and the columns; (3) the obvious curves at the bottom of the brackets used with the lowest purlins within the eaves; and (4) nanmu employed for the wooden frame, with some members made of hardwood pine. 11. ' Added-shoulder' (zengjian) is the triangular part of an horizontal architecture linking and the joint with the top of a pillar. 12. Hezi is a kind of decorative pattern used in decorative polychrome painting for long timber members in between two gutou at both ends. See from Jiang, Guangquan. 2005 now remains. Today, the six bays in the south of the surrounding building at the passageway at the rear of the western side hall are as follows: the wooden frames of the front porch are painted with oil paint, and they do not have decorative polychrome painting; that is different from the front porch of the six bays in the south of the eastern surrounding building, which is completely covered with decorative polychrome painting. Hence, it may be inferred that when the 18 bays of colonnades were added, the six bays in the south of the western surrounding building were not connected by colonnades. 23. See Zhu 2003. The text translates as: 'On the 5 th day of the 8 th month of the 7 th year of Yongzheng (1729), interior fixtures of the western main building and the western surrounding building were altered. ' 24. A layer of green pigment is found on the plaster base under the gutou at the northern end of the architrave of the northern central bay on the eastern gable side of the three bays at the centre of the main hall. Analysis shows the pigment to be malachite. 25. The pattern of hooped gutou developed in the early and the middle Qianlong period; it was originally used in the hexi-caihua of some religious architecture. . 'It was estimated that 77 liang and 9 qian of pink gold is needed to make the gold foil; 70 liang of pink gold was received from the Storage Office; 64 liang, 6 qian, 2 fen, and 4 li of pink gold was actually used; 5 liang, 3 qian, 7 fen, and 6 li of pink gold remains.' (liang, qian, fen, and li are all weight measurement units.) 29. Quanzong 05, Zou'an Vol. 0871, No. 012, Zou'an 05-0871-012 (Compiled Vol. 64039) 30. The outer side of the eave from the 7 th to the 12 th bay in the south of the eastern surrounding building. 31. Passion fruit ointment was a classic tonic in the dietetic invigoration plan of Empress Dowager Cixi. It is effective in treating such conditions as neuralgia, insomnia, menstrual pain, and diarrhea. As a floral decorative pattern, passion fruit was used on utensils from quite early in the history of China; it was widely used in architectural decorations, decorative polychrome painting, and interior fixtures in the Ming and Qing dynasties. The passion fruit pattern prevailed during the reign of the Qianlong emperor, and it became an exclusive pattern of the imperial household; it was forbidden for ordinary citizens to use it.