It all started with a painting of Queen Anne. After many years spent in storage, this anonymous oil canvas was recently cleaned and restored by Jenny Williamson, painting conservator at the Glynn Vivian Art Gallery (GVAG) in Swansea, UK. The portrait could not be dated correctly and the painter was unknown. There are no dates on the canvas or its labels. Ms. Williamson’s work brought back to life the portrait and vibrant colors of pigments typically used by artists in the early 18th century. But the question remained of the painting’s author – a very difficult challenge that only period experts can solve with the help of archives and analytical chemistry.
This challenge soon captured the interest of Dr. Cecile Charbonneau, Dr. Ann Hunter and Katie Hebborn, a team of scientists at the Faculty of Science and Engineering at Swansea University who share common passions for chemistry and fine arts. The team of four has been working together for a couple years to determine the chemical nature of pigments found in the painting in the hope of revealing clues to elucidate the identity of the painter. A variety of analytical techniques were focused on studying the blue pigment found in the dress of the young Queen Anne. A recent breakthrough enabled by mass spectrometry inspired a cross-disciplinary exhibition hosted by the GVAG and a supporting film documentary which tells the journey of their investigation. The current exhibition covers multiple aspects of the work carried out on the painting and explores associated scientific and historical concepts.
In this article, Dr. Charbonneau and Ms. Williamson tell us about their collaboration and their fascinating work at the interface of art and chemistry.
Tell us how this collaboration was brought to life?
Dr. Charbonneau: My research focuses on the synthesis and characterization of more sustainable materials and the development of low carbon routes for their processing into functional coatings that contribute towards the manufacture of energy harnessing and conversion technologies. I also teach the fundamentals of materials science at Swansea University. But my first and career decisive scientific research experience happened at the C2RMF, the research center affiliated to the Louvre museum in Paris. I always dreamt to come back to forensic sciences in the fields of arts and archeology.
A few years later, this dream came true when I met Jenny Williamson, art conservator at the GVAG in Swansea. Jenny was then working on the restoration of an oil canvas figuring young Queen Anne, looking to gain information on the chemical nature of the blue pigment used in the painting of Queen Anne’s drapery to find clues related to the dating of the canvas. Having built skills in the analysis of inorganic pigments, I offered to investigate small samples recovered as part of the restoration work. The investigation of the blue pigment turned out to be far from trivial and required the deployment of several analytical techniques (such as electron microscopy, Raman spectroscopy, mass spectrometry, etc.) and encouraged me to seek expertise in other branches of analytical chemistry. A team of arts and science enthusiastics progressively came together to solve the mystery of the blue pigment. Having finally solved the question of the blue pigment, we decided to tell the story of our multi-disciplinary collaboration and present our findings in the form of an exhibition that recently opened at the GVAG.
How does microscopy support your efforts?
Dr. Charbonneau: Microscopy played a very important role in various aspects of our investigation. To start with, optical microscopy made it possible to visualize the layered structure of very small samples recovered during the restoration. Cross-sections were made from the samples which were embedded in resin and cut through to reveal the layers, showing the pigment particles:
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Sample of paint taken from the blue drape and the pink dress. Cross-section made and photographed by Hannah Tempest.
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Sample of paint taken from the sky. Cross-section made and photographed by Hannah Tempest.
One of the findings associated to this was the use of a dark brown background layer applied on top of the ground. Backgrounds are of interest because they vary across artists and can be used to add evidence towards the attribution of a painting. These observations also made it possible to identify areas of interest for further analysis and optimize the sample preparation for electron microscopy imaging. An advantage of electron microscopy is that it allows much higher magnification than optical microscopy; however, it does not resolve the colors of the sample, making it a challenge to identify different layers or components of the samples. Hence, both techniques were very complementary. In our study, electron microscopy imaging, combined with elemental analysis made it possible to visualize fine white pigments of lead carbonate, also known as lead white, used to produce the light blue tint of the drapery. The darker and soft texture of material surrounding these white pigments also provided a hint on the organic nature of the blue pigment, which was later confirmed by mass spectrometry.
These electron microscopy images have been taken using the ZEISS EVO MA 25. Both represent one of our key samples, collected off the painting during its restoration. It shows a cross-section of all the different layers applied on the canvas. From left to right: the ground (rich in lead-Pb), a dark brown layer containing high contents of calcium, a dark blue layer (appears dark on the image), and finally the light blue layer (appears paler due to the presence of lead):
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This image was acquired using backscattered electrons. The contrasts on this image are related to the weight of elements present in the sample with heavier elements appearing brighter and lighter elements appearing darker.
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The chemical composition (EDS image) of these layers was investigated using energy dispersive spectroscopy, made possible with an Oxford Instrument detector installed on the ZEISS EVO 25 electron microscope. Each color is associated to the presence of Pb (blue), Ca (pink), and Si (yellow), respectively.
Which analytical techniques are you using?
Dr. Charbonneau: In addition to microscopy, Raman Spectroscopy was applied to samples recovered from the painting and to blue pigments of known compounds and chemical composition, e.g. reference materials. The matching of Raman peaks collected from the samples with that of known blue pigments can make it possible to identify the chemical nature of the blue pigment present in the painting. But it was challenging to collect any signal of the painting’s samples because of their rough topology. In addition, the reference indigo pigment provided very low Raman signal which made it difficult to identify all characteristic Raman peaks for this material. Despite these challenges, it was possible to match two Raman peaks collected from a sample with that of the reference indigo pigment. This was our first clue towards the chemical nature of the painting’s blue pigment. But we needed complementary analysis to confirm this hypothesis. Residues of the painting samples were then analyzed by mass spectrometry at the National Mass Spectrometry Facility, a work supported by Beacon+, which confirmed the blue pigment to be indigo.
What were your findings?
Ms. Williamson: After exhaustive research into the artist and sitter in the portrait our art historian has come to the conclusion that the painter of the work is very likely to be Michael Dahl. However, he has looked closely at the works considered to be ‘studio of Dahl’ and, on the whole, in his opinion, they do not match the quality of this painting. Another interesting point is that the sitter is almost certainly not Princess Anne but very likely to be associated with the Ellenborough family. This will be almost impossible to prove as records are not available. According to some of the experts many portraits had the status of the sitter ‘upgraded’ to enhance the sale price and this would appear to be the case here, too. Nevertheless, the portrait represents a piece of this fascinating history of the workings of the art market in the 19th century.
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Ms. Williamson uses a microscope to determine which process and techniques will be best suited for the piece. -
Before she starts to restore the painting she needs to clean it and remove discolored varnish layers. -
After the outer layers are removed, the painting can be restored.
“I hadn’t realized before, how many ways there are to look at the painting, and how each would give us different information. I feel that now we are going to have a whole new level of understanding and insight into this painting.”
Jenny Williamson
Tell us more about the current exhibition and the planned educational activities.
Ms. Williamson: The exhibition Indigo: Collections, Conservation, Chemistry covers multiple aspects of the work carried out on the painting and explores associated scientific and historical concepts. Visitors will first be introduced to the story of the canvas and witness the conservation work carried out with comparative photographs taken before and after the restoration of the painting. This will be immediately followed by the painting itself. Moving on, the story of our scientific investigation and the deployment of various analytical tools used to unravel the nature of the blue pigment will be presented. The origin of the blue color in the indigo pigment will be explained from a scientific point of view whilst it will also be presented in the context of a timeline placing the use of various blue pigments throughout history. A section of the exhibition is dedicated to the observation of samples prepared for cross-section observations. Visitors will be invited to observe these samples themselves using a ZEISS stereo microscope. They will be guided through and encouraged to compare their observations to electron microscope images of the same samples provided in the form of large prints. Finally, visitors will be invited to consider parallels between multilayered coating systems, as well as the value of skills developed to observe industrial coatings when transferred to the discipline of fine arts forensic investigation.
How do you think the interactive exhibit will help inspire another generation in microscopy?
Dr. Charbonneau: The exhibit displays a variety of microscopy images acquired during the forensic investigation of the samples and illustrates the power of scientific imaging in unravelling mysteries of the past. It also comprises an interactive space where visitors will be invited to observe samples of paintings using a ZEISS Stemi 305. This will encourage them to consider the fine layered structure of an oil canvas and experience the excitement generated by forensic analysis.
Ms. Williamson: The exhibition is cross-disciplinary: it presents the conservation and history of the portrait; scientific themes including the chemical nature of pigments, their color, their origin and which periods they were used in painting; and art conservation materials and techniques. Students can consider the variety of careers available that rely on the knowledge and application of chemical sciences. A guided walk through the exhibition will highlight our key scientific findings. Finally, our project aims to demonstrate the value of cross-disciplinary collaborations to a wide public whilst nurturing interest for chemistry through the fields of arts and conservation.
16 September 2021 – 27 February 2022
The exhibition, ‘Indigo: Collections, Conservation, and Chemistry’ at Glynn Vivian Art Gallery is part of the permanent collection displays. The exhibition revolves around the portrait painting of a young woman from the court of Queen Anne, from the Richard Glynn Vivian Bequest of 1911. Other items from the permanent collection enhance the display.
Through the painting, and more specifically the use of the pigment color indigo, the display will explore the history of the period in which the painting was made, the chemical nature of pigments and paint recipes, along with art conservation materials, chemistry, and techniques. Viewers are encouraged to connect with these multiple aspects, in order to explore the importance of chemistry in arts and conservation as a unique tool in revealing secrets of the past.