China’s Lost Mural Paintings: New conservation research into ancient art

Tonia Eckfeld

China’s Lost Mural Paintings: New conservation research into ancient art

TAASA Review, 2016

Recent archaeological discoveries in Shaanxi Province are new shedding light on China’s ancient tradition of mural painting. In May 2014, the University of Melbourne’s Grimwade Centre for Cultural Materials Conservation (GCCMC) has formally partnered with the Shaanxi Provincial Institute of Archaeology (SPIA) to scientifically analyse these paintings and uncover lost knowledge about the technical history of Chinese mural painting....Read more

4 ecent archaeological discoveries in Shaanxi Province are providing new evidence of China’s ancient tradition of mural painting. In May 2014, the University of Melbourne’s Grimwade Centre for Cultural Materials Conservation (Grimwade Centre) formally partnered with the Shaanxi Provincial Institute of Archaeology (SPIA). Through its focus on the materials and techniques of wall paintings in Shaanxi Province, this collaboration is revealing information about the technical history of Chinese mural painting, and providing new data to inform mural painting interpretation and conservation. This bilateral project has seen the strengthening of working relationships, the identifcation of shared research questions, the development of research approaches and preliminary outcomes of analytical studies, as well as cross-cultural exchange amongst conservation, archaeology and art history professionals and students. China’s lost mural paintings As highlighted by Professor Zhou Tianyou at the opening of the Second Qujiang Forum on Mural Painting in Xi’an in 2015, the history of Chinese ink brush painting is well known, but there is a lack of equivalent scholarship about Chinese mural painting. The problem is that mural painting is integrally tied to architecture and the demise of historical buildings through fre, rot and ruin also destroys the mural paintings that decorate them. In this way the signifcant tradition of Chinese mural painting in the pre-Ming period (pre-1368), recorded in historical Chinese texts, has largely been lost from the material record. Historical textual records in which some of these lost paintings are documented include Zhu Qingxuan’s Tang chao minghua lu (Record of Famous Paintings of the Tang Dynasty, written c.840) naming artists and important mural paintings in palaces, government buildings, temples and elite mansions, and Zhang Yanyuan’s Lidai minghua ji (Record of Famous Paintings of All the Dynasties, compiled c.847) describing important mural paintings. Such documentary sources are useful as a catalogue of paintings that have been lost and a touchstone for contextualising newly discovered paintings from historical periods. From the early 1950s, such texts were translated into English, making them more accessible internationally. The loss from the visual record of works by masters such as Tang dynasty (618-907) Yan Liben (c.600-673), Li Sixun (650-716), Wu Daozi (680-c.760) or Han Gan (c.706-783) has left a serious void. Late 19th century discoveries of mural paintings in the Mogao Buddhist cave temples at Dunhuang and at other sites along the Silk Road have provided a large corpus of 4th to 14th century mural painting for appreciation and research. Grounded in Buddhist tradition and at the periphery of the Chinese empire, however, these stunning works provide only a partial view of China’s once immense and accomplished mural painting repertoire. Newly discovered evidence Shaanxi Province is a key region for material culture in China. It was a heartland for ancient civilisation and home to the capital cities of 13 dynastic states from the Zhou to the Tang (c.1046 BCE – 907 CE). Archaeological excavations in Shaanxi Province are revealing important evidence of mural paintings at major centres dating from all periods. Each year since the early 1950s, important buried mural painting sites have been discovered with the total number of paintings running into many hundreds. Since 2000 alone, more than 20 tombs with paintings have been excavated. Fresh discoveries provide opportunities to study mural paintings in their original locations and architectonic contexts, alongside contemporaneous artifacts and with associated textual inscriptions. The provenance of discovery enables clearer understanding of the artworks’ meaning and signifcance through their historical, political, philosophical and cultural contexts. A few examples are worth naming to illustrate their importance. The earliest known Chinese mural paintings date from 2000 BCE, and were recently found detached and on the lower registers of stone gateway walls at the ancient palatial city Shimao near Shenmu. Underground tombs are like time capsules of mural painting art. A Western Han dynasty (206 BCE – 25 CE) brick underground tomb on the campus of Jiaotong University reveals a well-preserved complete classical Chinese funerary mural program. Tang dynasty mural paintings in royal and elite tombs represent a technical and aesthetic high point in Chinese mural painting tradition. Tang paintings on plaster are exemplifed by murals inside the principal attendant tombs at Qianling belonging to Princess Yongtai, Crown Prince Zhanghuai and Crown Prince Yide (dating from 706, excavated in 1960 and 1971-72) and by those in the tomb of Tang Prime Minister Han Xiu and his wife (762), excavated in 2014 in the southern suburbs of Xi’an. An intact Song dynasty (960-1279) doctor’s brick tomb completely lined with well-preserved murals was excavated at Hancheng city in 2008 and is one of a number being carefully preserved in their entirety for study and technical analysis. On a technical level, these discoveries are facilitating innovative research approaches. Conventionally, archaeologists, conservators, R CHINA’S LOST MURAL PAINTINGS: AUSTRALIA-CHINA CONSERVATION RESEARCH TO REDISCOVER ANCIENT ART Tonia Eckfeld, Caroline Kyi, Nicole Tse and Alex Xiaofei Duan TAASA REVIEW VOLUME 25 NO.4 TOMB OCCUPANT WITH FEMALE FAMILY MEMBERS, MURAL PAINTING IN THE YUAN DYNASTY LUOGETAI TOMB. PHOTO: COURTESY OF SPIA

5 TAASA REVIEW VOLUME 25 NO.4 scientists, artists and art historians used different methodologies for investigating mural paintings, materials and techniques, and contributed different information, leaving some key questions unanswered. At SPIA, broad integrated approaches are now emerging under the Directorship of Professor Wang Weilin so that multi-disciplinary teams work together, sharing knowledge and insights. Employing this approach, examination of the materials and techniques exhibited in the mural paintings begins in situ at the archaeology excavation site utilising standard physical and chemical examination, scientifc instrumental analysis and technical art history research. Furthermore, art historical and conservation experts provide connoisseurs’ knowledge supplementing primary archaeological research fndings. The Australia-China collaboration The SPIA mural painting conservation team has worked for many decades to protect these treasures with signifcant success, mastering both the detachment of the murals from their original archaeological locations as well as their conservation. Previous partnerships have been important in supporting this work, including between SPIA and the Roman-German Central Museum of Mainz, and individual scholars such as Australian Tonia Eckfeld, working closely with SPIA on archaeological site and mural painting research since the mid-1990s. In 2014, the Grimwade Centre began participating in Chinese mural painting conservation through expert exchanges, symposia, feldwork and joint research in China and Australia. In 2015 these activities expanded to include an internship program with SPIA facilitating University of Melbourne Masters level conservation interns to work at SPIA’s laboratories for training and to undertake practical conservation of detached mural paintings. The involvement of graduate students adds to the project’s body of knowledge and provides interns with an integrated cross-cultural professional learning experience. The SPIA-Grimwade Centre cooperation is comprised of a multi-disciplinary team with archaeologists, materials conservators and art historians who begin studying the mural paintings at the excavation site from the point of discovery. There are a number of challenging questions about Chinese mural paintings that remain to be answered. These include: the identity of the painters and materials used; particular workshop practices, techniques and styles; defning the different mural painting traditions or schools, and what this information tell us about the lost corpus of above ground mural paintings. To develop new insights, SPIA and the Grimwade Centre are making reciprocal visits to Shaanxi Province and the University of Melbourne each year for scientifc and technical analysis, feldwork, training, expert symposia, lectures for conservation professionals and teaching university students. In this way, detailed knowledge of particular materials and manufacturing techniques is also informing new techniques and approaches in the conservation of ancient Chinese mural paintings. Mural painting case studies A key step in the project has been the development of an historic mural painting ‘sample bank’ held at SPIA. The joint team has developed approaches to the methodical collection, archiving and analysis of detached and fragmentary mural painting material, including cross-referencing of data on mural material from different sites. Recent investigations in China and Australia have centred on two large wall paintings schemes from recently discovered underground tombs. The frst is from a Yuan dynasty (1271-1368) tomb discovered in 2014 in Luogetai Village in Hengshan County in north Shaanxi Province. The stone tomb has a rectangular entrance and an octagonal chamber with a domed roof. (Figure 1) The whole tomb is 6.1m long and 2.8m high with a 2.3m diameter dome. A complex scheme of painted murals covers the tomb’s plaster-lined walls. The scheme comprises celestial scenes in the upper register, images of the tomb owner surrounded by scenes of flial piety in the middle and scenes of earthly pleasures such as wine and tea preparation, and musical performance in the lower register. In Xi’an during 2015, intern masters students from the Grimwade Centre worked with colleagues at SPIA on a scene from the Luogetai tomb depicting wine preparation. (Figure 2) The interns were involved in the treatment testing, treatment and general conservation of this part of the mural painting scheme. Scientifc investigation at the University of Melbourne focused on mural painting pigments and binders from the Tang dynasty tomb M68 discovered in 2014 at the Taipingbao site, Jingyang County, Xianyang, Shaanxi Province. Originally, a spirit road lead to the tomb with a colossal 30m diameter rammed earth mound marking the site. Underground, the tomb extended 35m in length and had a depth of 10m with a long entry passage, fve side niches for the storage of burial goods, fve ventilation shafts and a single coffn chamber, all denoting it as a tomb of exceptionally high status. Surviving mural paintings on the tomb passage walls indicate an extravagant pictorial program including guards with halberds, a male civil offcial and an attendant woman, two Indian Buddhist monks, a horse and groom, a riderless horse and three directional animals – dragon, tiger and red bird. (Figures 3 and 4) The murals are bright, richly coloured and skilfully painted in a lively style indicative of a date in the frst half of the 8th century. Scientifc analysis During excavations in 2014, SPIA experts studied the Taipingbao tomb M68’s wall paintings using a range of non-invasive techniques including infrared examination, WINE PREPARATION SCENE, MURAL PAINTING IN THE YUAN DYNASTY LUOGETAI TOMB. PHOTO: COURTESY OF SPIA

C H I N A’ S L O S T M U R A L PA I N T I N G S : A U S T R A L I A - C H I N A C O N S E R V AT I O N RESEARCH TO REDISCOVER ANCIENT ART Tonia Eckfeld, Caroline Kyi, Nicole Tse and Alex Xiaofei Duan TOMB OCCUPANT WITH FEMALE FAMILY MEMBERS, MURAL PAINTING IN THE YUAN DYNASTY LUOGETAI TOMB. PHOTO: COURTESY OF SPIA ecent archaeological discoveries in Shaanxi Province are providing new evidence of China’s ancient tradition of mural painting. In May 2014, the University of Melbourne’s Grimwade Centre for Cultural Materials Conservation (Grimwade Centre) formally partnered with the Shaanxi Provincial Institute of Archaeology (SPIA). Through its focus on the materials and techniques of wall paintings in Shaanxi Province, this collaboration is revealing information about the technical history of Chinese mural painting, and providing new data to inform mural painting interpretation and conservation. R This bilateral project has seen the strengthening of working relationships, the identification of shared research questions, the development of research approaches and preliminary outcomes of analytical studies, as well as cross-cultural exchange amongst conservation, archaeology and art history professionals and students. China’s lost mural paintings As highlighted by Professor Zhou Tianyou at the opening of the Second Qujiang Forum on Mural Painting in Xi’an in 2015, the history of Chinese ink brush painting is well known, but there is a lack of equivalent scholarship about Chinese mural painting. The problem is that mural painting is integrally tied to architecture and the demise of historical buildings through fire, rot and ruin also destroys the mural paintings that decorate them. In this way the significant tradition of Chinese mural painting in the pre-Ming period (pre-1368), recorded in historical Chinese texts, has largely been lost from the material record. Historical textual records in which some of these lost paintings are documented include Zhu Qingxuan’s Tang chao minghua lu (Record of Famous Paintings of the Tang Dynasty, written c.840) naming artists and important mural paintings in palaces, government buildings, temples and elite mansions, and Zhang Yanyuan’s Lidai minghua ji (Record of Famous Paintings of All the Dynasties, compiled c.847) describing important mural paintings. Such documentary sources are useful as a catalogue of paintings that have been lost and a touchstone for contextualising newly discovered paintings from historical periods. From the early 1950s, such texts were translated into English, making them more accessible internationally. 4 The loss from the visual record of works by masters such as Tang dynasty (618-907) Yan Liben (c.600-673), Li Sixun (650-716), Wu Daozi (680-c.760) or Han Gan (c.706-783) has left a serious void. Late 19th century discoveries of mural paintings in the Mogao Buddhist cave temples at Dunhuang and at other sites along the Silk Road have provided a large corpus of 4th to 14th century mural painting for appreciation and research. Grounded in Buddhist tradition and at the periphery of the Chinese empire, however, these stunning works provide only a partial view of China’s once immense and accomplished mural painting repertoire. Newly discovered evidence Shaanxi Province is a key region for material culture in China. It was a heartland for ancient civilisation and home to the capital cities of 13 dynastic states from the Zhou to the Tang (c.1046 BCE – 907 CE). Archaeological excavations in Shaanxi Province are revealing important evidence of mural paintings at major centres dating from all periods. Each year since the early 1950s, important buried mural painting sites have been discovered with the total number of paintings running into many hundreds. Since 2000 alone, more than 20 tombs with paintings have been excavated. Fresh discoveries provide opportunities to study mural paintings in their original locations and architectonic contexts, alongside contemporaneous artifacts and with associated textual inscriptions. The provenance of discovery enables clearer understanding of the artworks’ meaning and significance through their historical, political, philosophical and cultural contexts. A few examples are worth naming to illustrate their importance. The earliest known Chinese mural paintings date from 2000 BCE, and were recently found detached and on the lower registers of stone gateway walls at the ancient palatial city Shimao near Shenmu. Underground tombs are like time capsules of mural painting art. A Western Han dynasty (206 BCE – 25 CE) brick underground tomb on the campus of Jiaotong University reveals a well-preserved complete classical Chinese funerary mural program. Tang dynasty mural paintings in royal and elite tombs represent a technical and aesthetic high point in Chinese mural painting tradition. Tang paintings on plaster are exemplified by murals inside the principal attendant tombs at Qianling belonging to Princess Yongtai, Crown Prince Zhanghuai and Crown Prince Yide (dating from 706, excavated in 1960 and 1971-72) and by those in the tomb of Tang Prime Minister Han Xiu and his wife (762), excavated in 2014 in the southern suburbs of Xi’an. An intact Song dynasty (960-1279) doctor’s brick tomb completely lined with well-preserved murals was excavated at Hancheng city in 2008 and is one of a number being carefully preserved in their entirety for study and technical analysis. On a technical level, these discoveries are facilitating innovative research approaches. Conventionally, archaeologists, conservators, TA A S A R E V I E W V O L U M E 2 5 N O. 4 WINE PREPARATION SCENE, MURAL PAINTING IN THE YUAN DYNASTY LUOGETAI TOMB. PHOTO: COURTESY OF SPIA scientists, artists and art historians used different methodologies for investigating mural paintings, materials and techniques, and contributed different information, leaving some key questions unanswered. At SPIA, broad integrated approaches are now emerging under the Directorship of Professor Wang Weilin so that multi-disciplinary teams work together, sharing knowledge and insights. Employing this approach, examination of the materials and techniques exhibited in the mural paintings begins in situ at the archaeology excavation site utilising standard physical and chemical examination, scientific instrumental analysis and technical art history research. Furthermore, art historical and conservation experts provide connoisseurs’ knowledge supplementing primary archaeological research findings. The Australia-China collaboration The SPIA mural painting conservation team has worked for many decades to protect these treasures with significant success, mastering both the detachment of the murals from their original archaeological locations as well as their conservation. Previous partnerships have been important in supporting this work, including between SPIA and the Roman-German Central Museum of Mainz, and individual scholars such as Australian Tonia Eckfeld, working closely with SPIA on archaeological site and mural painting research since the mid-1990s. In 2014, the Grimwade Centre began participating in Chinese mural painting conservation through expert exchanges, symposia, fieldwork and joint research in China and Australia. In 2015 these activities expanded to include an internship program with SPIA facilitating University of Melbourne Masters level conservation interns to work at SPIA’s laboratories for training and to undertake practical conservation of detached mural paintings. The involvement of graduate students adds to the project’s body of knowledge and provides interns with an integrated cross-cultural professional learning experience. The SPIA-Grimwade Centre cooperation is comprised of a multi-disciplinary team with archaeologists, materials conservators and art historians who begin studying the mural paintings at the excavation site from the point of discovery. There are a number of challenging questions about Chinese mural paintings that remain to be answered. These include: the identity of the painters and materials used; particular workshop TA A S A R E V I E W V O L U M E 2 5 N O. 4 practices, techniques and styles; defining the different mural painting traditions or schools, and what this information tell us about the lost corpus of above ground mural paintings. To develop new insights, SPIA and the Grimwade Centre are making reciprocal visits to Shaanxi Province and the University of Melbourne each year for scientific and technical analysis, fieldwork, training, expert symposia, lectures for conservation professionals and teaching university students. In this way, detailed knowledge of particular materials and manufacturing techniques is also informing new techniques and approaches in the conservation of ancient Chinese mural paintings. Mural painting case studies A key step in the project has been the development of an historic mural painting ‘sample bank’ held at SPIA. The joint team has developed approaches to the methodical collection, archiving and analysis of detached and fragmentary mural painting material, including cross-referencing of data on mural material from different sites. Recent investigations in China and Australia have centred on two large wall paintings schemes from recently discovered underground tombs. The first is from a Yuan dynasty (1271-1368) tomb discovered in 2014 in Luogetai Village in Hengshan County in north Shaanxi Province. The stone tomb has a rectangular entrance and an octagonal chamber with a domed roof. (Figure 1) The whole tomb is 6.1m long and 2.8m high with a 2.3m diameter dome. A complex scheme of painted murals covers the tomb’s plaster-lined walls. The scheme comprises celestial scenes in the upper register, images of the tomb owner surrounded by scenes of filial piety in the middle and scenes of earthly pleasures such as wine and tea preparation, and musical performance in the lower register. In Xi’an during 2015, intern masters students from the Grimwade Centre worked with colleagues at SPIA on a scene from the Luogetai tomb depicting wine preparation. (Figure 2) The interns were involved in the treatment testing, treatment and general conservation of this part of the mural painting scheme. Scientific investigation at the University of Melbourne focused on mural painting pigments and binders from the Tang dynasty tomb M68 discovered in 2014 at the Taipingbao site, Jingyang County, Xianyang, Shaanxi Province. Originally, a spirit road lead to the tomb with a colossal 30m diameter rammed earth mound marking the site. Underground, the tomb extended 35m in length and had a depth of 10m with a long entry passage, five side niches for the storage of burial goods, five ventilation shafts and a single coffin chamber, all denoting it as a tomb of exceptionally high status. Surviving mural paintings on the tomb passage walls indicate an extravagant pictorial program including guards with halberds, a male civil official and an attendant woman, two Indian Buddhist monks, a horse and groom, a riderless horse and three directional animals – dragon, tiger and red bird. (Figures 3 and 4) The murals are bright, richly coloured and skilfully painted in a lively style indicative of a date in the first half of the 8th century. Scientific analysis During excavations in 2014, SPIA experts studied the Taipingbao tomb M68’s wall paintings using a range of non-invasive techniques including infrared examination, 5 INDIAN BUDDHIST MONK, MURAL PAINTING IN THE TANG OFFICIAL, MURAL PAINTING IN THE TANG DYNASTY DYNASTY TAIPINGBAO TOMB M68 (EAST WALL OF THE TOMB TAIPINGBAO TOMB M68 (EAST WALL OF THE TOMB PASSAGE). PASSAGE). PHOTOS: COURTESY OF SPIA PHOTOS: COURTESY OF SPIA prepared from materials of the previous phases of scientific analysis. The SPIA-Grimwade Centre approach to research has been a consultative and iterative process, accommodating revisions to research hypotheses and research methodologies. Continued research will yield more information on the properties of Chinese mural paintings, answer the big questions outlined in this article, situate mural painting tradition in its rightful place of importance within art historical discourse, and support optimal conservation methods to protect these murals for future generations. Professor Tonia Eckfeld is Principal Fellow and Project Leader, School of Historical and Philosophical Studies, University of Melbourne. Dr Caroline Kyi is a PostDoctoral Fellow, The Grimwade Centre for Cultural Materials Conservation, University of Melbourne. Dr Nicole Tse is Senior Lecturer, The Grimwade Centre for Raman spectroscopy and X-ray fluorescence (XRF). Building on SPIA’s in situ investigations of the tomb, laboratory analysis was undertaken to further characterise materials and investigate the mural painting techniques. In 2015, fragments of the murals were brought to the Grimwade Centre. Investigations over 10 days employed laboratory-based techniques including Fourier Transform Infrared Spectroscopy (FTIR) in the investigation of organic materials, and X-ray fluorescence (XRF) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) in the investigation of inorganic materials. Previous XRF analysis conducted by SPIA, detected key elements: calcium, copper, iron and lead. The presence of calcium, in association with other signature elements, can indicate the presence of calcium carbonate used in fresco technique. Although fresco painting technique is highly durable, the palette is limited due to the alkaline conditions created during production when certain pigments become unstable and therefore unsuitable for fresco application. These pigments are more commonly combined with a binder to form a paint mixture that is then applied a secco - that is, to a dry plaster layer. Therefore, in order to achieve a desired range of colours and a measure of durability, artists may combine fresco and secco techniques. During investigations at the Grimwade Centre using XRF and ICP-OES, elemental iron, indicative of common iron-based pigments, and red and yellow ochre, were detected in areas of red polychrome. ICP-OES supported quantification of the amount of 6 Cultural Materials Conservation, University iron in the samples and enabled researchers to distinguish between iron present in the pigment or in the soil adhering to the surface as a result of burial. of Melbourne. Dr Alex Xiaofei Duan is Academic Samples of green pigment were also tested using XRF and ICP-OES, and copper was detected using both techniques. ICP-OES analysis indicated that the levels of copper were particularly high when compared to other elements, excluding iron. This sensitive investigative technique found low levels of lead in a sample of green pigment as well as in a sample of orange. REFERENCES Specialist, Trace analysis for chemical, earth and environmental sciences, Faculty of Science, University of Melbourne. Acker, William, 1954. Some T’ang and Pre-T’ang Texts on Chinese Painting, E.J.Brill, Leiden; and Vol.2, 1974. Eckfeld, Tonia, 2005. Imperial Tombs in Tang China 618-907, The Politics of Paradise, Routledge Curzon, London and New York Shaanxi Provincial Institute of Archaeology, 2009. Conservation and Restoration of Murals from Tombs of the Han and Tang Dynasties, San Qin Publishing, Xi’an Zhu Zhanyun & Tonia Eckfeld, 2016. ‘The Development of Conservation Practices in China from the 1980s to the Present’, AICCM Bulletin, 37:1, pp. 26-34 While ochre pigments occur commonly in the historical fresco palette, green, often derived from copper-based pigments, and lead based pigments such as lead white are less suitable for fresco and are commonly applied with a binder. The detection of copper and lead in pigment materials from the samples provides evidence to support the use of secco technique in the painting of the Taipingbao murals. Additional analysis using FTIR was performed to look for the presence of organic materials indicative of a binder, but the findings were inconclusive. Compared with inorganic materials, the analysis of organic materials is compromised by their rate of degradation Due to the alteration of materials over time, analytical challenges are often encountered in developing scientific research approaches for mural paintings. To support the ongoing investigations into Chinese mural painting techniques, in particular the study of aged binders, the Grimwade is currently researching the accelerated aging of samples TA A S A R E V I E W V O L U M E 2 5 N O. 4

Bài Team-Based Learning4-2: Quản lý các vấn đề thường gặp liên quan đến nửa đầu thai kỳ Bài giảng trực tuyến Human Chorionic Gonadotropin (hCG): động học và các vấn đề có liên quan © Bộ mônPhụ Sản,KhoaY, ĐạihọcY DượcTP.Hồ ChíMinh.Tác giả giữ bản quyền 1 Bài Team-Based Learning4-2: Quản lý các vấn đề thường gặp liên quan đến nửa đầu thai kỳ Human Chorionic Gonadotropin (hCG): động học và các vấn đề có liên quan. Mục tiêu bài giảng Sau khi học xong, sinh viên có khả năng: 1. Trình bày được cấu tạo và sinh lý của hCG trong thai kỳ 2. Trình bày được động học hCG trong thai kỳ 3. Diễn giải được kết quả hCG và diễn tiến thai kỳ NGUỒN GỐC VÀ TÁC DỤNG CỦA hCG (human Chorionic Gonadotropin) Cấu trúc của một phân tử hCG bao gồm 2 chuỗi α và β liên kết polypeptide. Chuỗi β tạo ra đặc tính sinh học cho phân tử hCG. hCG là một glycoprotein có trọng lượng phân tử 36000-40000 Da. Đây là hormone có chứa nhiều liên kết carbonhydrate nhất trong các hormone ở loài người. Chính nhờ số lượng liên kết carbonhydrate lớn và đoạn C-terminal mà hCG có thời gian bán hủy lên tới khoảng 36 giờ. Mỗi phân tử hCG bao gồm 2 tiểu đơn vị α và β không tương đồng với nhau. Chuỗi α gồm 92 acid amin được mã hóa bởi 1 gene trên nhiễm sắc thể 6 và chuỗi β gồm 145 acid amin được mã hóa bởi 6 gene riêng rẽ trên nhiễm sắc thể 19. Hai tiểu đơn vị này được kết hợp với nhau tại lưới nội sinh chất bằng các cầu polypeptide, nếu tách rời nhau thì chúng không thể gắn vào thụ thể LH và có ít hoạt tính sinh học. Cấu trúc chuỗi α của phân tử hCG tương tự chuỗi α của các glycoprotein khác là LH, FSH và TSH nhưng cấu trúc chuỗi β của chúng lại khác nhau, chính sự khác biệt của chuỗi β quy định hoạt tính sinh học riêng cho từng loại glycoprotein. Trong đó, β-hCG gần giống với β-LH nên hCG có hoạt tính sinh học và miễn dịch gần giống với LH. hCG được sản xuất chủ yếu bởi các hội bào nuôi và thường là dấu hiệu có thai sinh hóa. Khi thai dưới 5 tuần tuổi, hCG được sản xuất ở cả nguyên bào nuôi và hội bào nuôi. Đến khi nồng độ hCG trong huyết tương mẹ đạt đỉnh, hCG chỉ còn được sản xuất bởi các hội bào nuôi. Ngoài bánh nhau, thận, tuyến yên và một số mô khác của thai cũng có thể sản xuất ra hCG. Chorionic gonadotropin cũng được tìm thấy với một nồng độ rất nhỏ ở đàn ông và phụ nữ không có thai, có lẽ chủ yếu sản sinh ở tuyến yên trước. hCG cũng được tìm thấy trong bệnh lý tân sinh nguyên bào nuôi hoặc trong các bệnh lý ác tính không liên quan đến nguyên bào nuôi. Tuy nhiên, việc tìm thấy hCG trong huyết tương hay trong nước tiểu một người phụ nữ trong độ tuổi sinh sản thường là dấu hiệu sinh hoá của thai kỳ. Phân tử hCG có thể tồn tại ở nhiều dạng khác nhau trong huyết tương và trong nước tiểu. Các cầu liên kết polypeptide có thể bị gẫy làm phá vỡ cấu trúc hCG, hiện tượng này tăng theo tuổi thai. Ngoài ra, phân tử hCG còn có thể trải qua quá trình đứt gãy, phân ly và thoái giáng tạo thành nhiều dạng hCG khác nhau lưu hành trong huyết tương: non-nicked hCG (hCG toàn phần không đứt gãy), nicked hCG (hCG toàn phần đứt gãy), free α-hCG (α-hCG tự do), non-nicked free β-hCG (β-hCG không đứt gãy, tự do), nicked free β-hCG (β-hCG đứt gãy, tự do), Β-core fragment (mảnh vỡ lõi β-hCG). Tỉ lệ các dạng hCG thay đổi tùy thuộc vào tuổi thai và vào bệnh lý của thai kỳ. Tùy vào từng mục đích mà người ta sẽ chọn khảo sát dạng lưu hành nào của hCG trong huyết tương. hCG có vai trò quan trọng trong việc duy trì hoàng thể thai kỳ. hCG hoạt động bằng cách gắn vào thụ thể LH. Cấu tạo chuỗi β-hCG có phần đầu gồm 121 amino acid giống với LH vì vậy có thể gắn lên cùng thụ thể LH nhưng với ái lực khác nhau. Đến nay, chức năng sinh học được biết rõ nhất của hCG là biến hoàng thể chu kỳ thành hoàng thể thai kỳ, duy trì hoàng thể thai kỳ trong tam cá nguyệt I và thúc đẩy hoàng thể sản xuất hormone steroid.Tuy nhiên, đây không phải là toàn bộ chức năng của hCG vì người ta nhận thấy hCG vẫn tiếp tục tăng sau khi hoàng thể thai kỳ đã thoái hóa. Chức năng khác được biết đến của hCG là kích thích tinh hoàn thai nhi sản xuất ra testosterone. Tại thời điểm thai nhi biệt hóa giới tính, hCG từ khối hội bào nuôi đi vào trong máu thai, nó có vai trò như một đỉnh LH kích thích tế bào Leydig và tổng hợp ra testosterone để biệt hóa giới tính nam. Trước 110 ngày tuổi thai (15-16 tuần), thai nhi không có mạch máu nối giữa hạ đồi – tuyến yên nên không có LH mà cần hCG để hoạt động. Ngoài ra, người ta cũng tìm thấy thụ thể của LH trên cơ trơn tử cung, hCG cũng kích thích hoàng thể sản xuất ra relaxin giúp giảm co thắt cơ trơn tử cung. hCG được sản xuất từ khối hội bào nuôi còn có thể tác động theo con đường cận tiết để thúc đầy sự phát triển chất nền nội mạc tử cung, tăng tạo mạch để hỗ trợ cho quá trình làm tổ. ĐỘNG HỌC CỦA hCG TRONG THAI KỲ hCG có thể tìm thấy trước khi trễ kinh, tăng dần đến đỉnh ở tuần thứ 8-10 của thai kỳ sau đó giảm dần. Ở thai kỳ bình thường có thể phát hiện hCG sau đỉnh LH 9-11 ngày tức là khoảng 8 ngày sau phóng noãn, và chỉ 1 ngày sau khi phôi làm tổ. Trước 6 tuần, nồng độ hCG tăng gấp đôi mỗi 2 ngày và đạt đỉnh ở tuần 8-10, có thể vào khoảng 100.000 mUI/ml. Sau đó, nồng độ hCG sẽ giảm dần và đạt cực tiểu tại thời điểm 16-20 tuần rồi giữ ổn định ở mức này đển cuối thai kỳ. Đường biểu diễn biến thiên nồng độ hCG trong nước tiểu của mẹ cũng đồng dạng với đường biểu diễn biến thiên nồng độ hCG trong huyết tương. Cần lưu ý là nồng độ hCG trong nước tiểu thay đổi không phụ thuộc vào thời điểm trong ngày mà phụ thuộc vào lưu lượng nước tiểu.

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China’s Lost Mural Paintings: New conservation research into ancient art