By Sarah Benrubi
Last November the 5th course given by IIC and the International Training Centre for Conservation (IIC-ITCC) took place in the Hospital for Conservation at the Palace Museum in Beijing. Following the previous courses on non-destructive analyses, preventive conservation, painting and paper, the 5th course was dedicated to scientific approaches to the conservation of ceramics and glass. Intensive courses and lectures were organized from 11th to 23rd November 2019.
Twenty-four participants were selected both from China and abroad. Chinese conservators from Beijing, Shanghai, Hong Kong, Jingdezhen, Shaanxi, Beijing, Sichuan, Zhejiang and Henan attended the course. Foreigners came from Cambodia, Iran, Serbia, the United Kingdom, Turkey, Lithuania, Singapore, Croatia, Germany, Greece and myself from Belgium.
All together we covered a broad overview of the field, working as conservators on archaeological sites, in public institutions, in conservation programs and sometimes for private clients. We work on archaeological items (underwater materials were well represented), decorative and contemporary art.
IIC-ITCC lecturers were specialists in the field of ceramics and glass: Sarah Staniforth (President Emeritus, IIC); Chandra Reedy (University of Delaware); Austin Nevin (University of Gothenburg); Norman Tennent (University of Texas at Dallas/University of Amsterdam); Frankie Halahan (Halahan Associates); and Yong Lei, Wusheng Wang and Ningchang Shi from The Palace Museum.
The course combined theoretical presentations and practical sessions which benefited from the exceptional scientific infrastructure and staff at the Hospital for Conservation.
Yong Lei described some research carried out in the laboratories: extensive databases on the composition of Chinese ceramic productions (Ge Ware project), technology research projects on black porcelain and an extensive survey on the origin and distribution of cobalt blue in early Ming Dynasty porcelain.
Sarah Staniforth introduced us to preventive conservation and the ten agents of deterioration. Practical observation and risk assessments were conducted by groups in different locations around the Forbidden City.
Austin Nevin led a course on non-destructive analyses for ceramics and glass; FTIR, Raman spectroscopy, X-ray fluorescence and X-ray diffraction were demonstrated. FTIR remains the analytical method of choice when it comes to the identification of conservation polymers and adhesives. For Raman spectroscopy, in practice, we realised the complexity of calibration parameters and its power for the identification of colourants. These are complex techniques that require great mastery for proper analysis of ceramic and glass materials. We were all familiar with portable XRF equipment, which we have used extensively to define the nature of chemical elements on many different types of artefacts. However, the detection of lighter elements is more difficult using XRF, making this technique of limited use when it comes to the analysis of glass composition—this limitation, however, can be partially overcome by working in a vacuum. In practice vacuum analysis avoids perturbation and makes lighter elements more visible (we were wondering how harmful this vacuum process could be for extremely thin or crizzled material). The last technique demonstrated, and probably the most impressive, was X-ray diffraction (XRD). An entire object was securely fixed in a transparent isolated box. Crystalline networks and molecules were detected using different X-ray sources and detectors. Some of these molecular structures can begin to appear only when ceramics are fired above specific temperatures. Indeed, XRD gave impressive results on ceramics without sampling, and we were able to signal from multiple points on the surface, thereby increasing the accuracy of our results. "
As you can imagine, this introduction to these techniques didn’t make us specialists, but gave us better knowledge for selecting which specialist or equipment we might use to answer specific conservation and research questions. As Norman Tennent highlighted, we can carry out analyses for many reasons, but this is not always necessary to properly treat an object.
Chandra Reedy gave us an introduction to thin-section petrography applied to ceramic materials. With many examples she explained the information we can gather from observations in plane-polarized light and cross-polarized light including the nature of the components, the origin of material, even the firing process, the quality of execution and manufacturing information. With her extensive collection of thin sections we had the opportunity to observe many different types of ceramic. We all wished for more time to observe and understand this collection more extensively.
Norman Tennent presented seven lectures based on research subjects in which he was involved with various institutions: glass and enamel composition (with a focus on laser ablation-inductively coupled plasma-mass spectrometry), deterioration of glass (with a focus on identification of ionic species on the surface of unstable glass), cleaning issues for glass and glazing, aging studies on a selection of polymers with optimal properties for glass conservation (including identifying and predicting the aging behaviour of polymers), the significance of refractive index in regard to glass restoration, and blue metamerism and glaze colour matching and analysis. Many case studies were also illustrated, helping us to understand the decision-making process in the implementation of complex and multi-problem treatments.
Frankie Halahan shared her experience by highlighting—through various presentations—a diversity of materials, techniques of production, forms of degradation and restoration techniques available to us.
Wusheng Wang showed us various conservation treatments carried out in China, and we were able to see that our professional practices, though in some cases separated by continents, are not as far apart as we might often think.
Finally, Ningchang Shi presented us with multiple fragments of ceramic materials. Where, in the West, we often group these materials under the generic category of celadon, Ningchang Shi helped us to recognize the different aesthetic and technological particularities characterizing the production of Ru, Guan, Longquan and Yue (and Mise Yue) ware.
We had an exhilarating break from these intense study days when we went to the Great Wall. We also had the
opportunity to experience wheel throwing and applying cobalt glazing on porcelain. The course was organized very efficiently, fostering connections and collaborations between the participants. The question sessions were also very helpful allowing all participants to interact and share individual knowledge and experiences with the whole group.
And what about the non-verbal re-cap that we participated in to summarise different aspects of the course!!! I prefer not to write about it, in order to leave a surprise for the next participants.
The next two IIC-ITCC courses will focus on built heritage conservation and metal conservation. So, stay tuned!
Sarah Benrubi has a master’s degree in the conservation of ceramics and glass (2003) from La Cambre Brussels, Belgium. She followed this with internships at The Corning Museum of Glass and The National Museum in Cardiff. Back in Belgium she was a post-graduated intern at the Royal Institute for Cultural Heritage. Since 2005 she has worked as a private conservator and in 2015 became the teacher responsible for the ceramics and glass conservation department at La Cambre.
(Read the full article in the April-May 2020 "News in Conservation" Issue 77, p. 48-52)