How Science is Keeping Old Master Paintings Alive

Image description: Rembrandt van Rijn – Homer

On 25 January this year, the journal Chemical Communications published a major breakthrough on a mystery that had hitherto perplexed the art world: why the Old Master Rembrandt van Rijn’s celebrated painting ‘Homer(1663) was coated in a thin white crust. The unknown composition and origin of the substance had been cumbersome for conservationists who were struggling to adequately preserve the painting without identifying the deposit. A collaboration of conservation scientists from the Mauritshuis, the Rijksmuseum, University of Amsterdam and scientists from Finden Ltd, UCL, and the Diamond Light Source, however, have finally decoded the answer. Key to deciphering the mystery was applying synchrotron radiation at the Diamond Light Source, the UK’s synchrotron located in Didcot, Oxfordshire.

But what is synchrotron radiation exactly and how did it solve the riddle of the ‘Homer’ painting? The Diamond Light Source – located in a unique toroidal building at the Harwell Science and Innovation Campus – contains a cyclic particle accelerator that is truly state-of-the-art. The technical machine produces synchrotron radiation that is 10,000 times more powerful in strength than a traditional microscope and accelerates electrons to speeds that emit light at 10 billion times brighter than our sun. This bright light is what enables scientists to study a wide band of specimens in miniscule depth from virus structures, jet engines, and even the chemical structures of Old Master paintings. As synchrotron radiation is potent at extrapolating the most information from a small, valuable sample, it is an ideal way to study delicate artwork and archaeological objects.

It is essential to understand the chemical reactions taking place on the canvases of Old Master paintings to guide conservation strategies

The scientists at Diamond took a micro-sample of paint from Rembrandt’s ‘Homer’ and imaged it using a method called ‘X-ray Diffraction Computed Tomography’ to take a 3D image of the chemical distribution throughout the paint stratigraphy. Upon investigation, the surface crust was identified as a complex alloy of lead sulphates such as the sulphur-rich minerals palmierite and anglesite. Furthermore, the microfocus X-ray beam revealed that, during the history of the painting, Rembrandt’s lead-containing paint was subject to reactions with atmospheric pollutants such as sulphur dioxide, thus forming the white crust that disfigures the painting. However, it is not just the surface of the painting that has suffered from entropy but also the layers of paint underneath: an analysis of the sulphur-lead ratios in the paint revealed lanarkite and leadhillite, indicating that the sulphur has permeated through the paint layers. Thus, there are in fact multiple chemical reactions taking place in the fabric of the painting.

The results derived from this incisive scan of Rembrandt’s ‘Homer’ – formation of sulphate-minerals, movement of lead through paint layers, and soap formation – not only reveal the painting’s chemical composition but also its tumultuous history, having been exposed to harsh environments before entering the care of the Mauritshuis collection. In their journal publication, researchers explain that the origin of the sulphur could be due to sulphur dioxide: ‘combustion from domestic heating in the past may have released sulphurous gases into the atmosphere, as did the industrial revolution’. A study of the surface crust alone using synchrotron radiation tells a variety of secrets about the painting and how it weathered the test of environmental challenges, providing valuable information for art historians.

Art conservation requires interdisciplinary collaboration with the sciences to ensure paintings’ survival

Rembrandt’s ‘Homer’ is only one example of how art conservation requires interdisciplinary collaboration with the sciences to ensure paintings’ survival. By nature fragile and irreplaceable, it is essential to understand the chemical reactions taking place on the canvases of Old Master paintings to guide conservation strategies. With newly acquired knowledge of how the chemical crust on ‘Homer’ developed, art conservators are now able to work towards preventing such crusts from degrading the painting in the future. Researchers can also begin engineering new restoration methods to ensure that museum visitors can continue enjoying Old Master works. Scientific technology (such as synchrotron radiation) thus validates the museum industry because by revealing the chemical reactions that are detrimental old paintings, they highlight the importance of stable museum conditions that house works of art properly.

The successful research at Diamond is particularly timely as 2019 commemorates 350 years since Rembrandt’s death. Celebration of his legacy continues in museums around the world throughout this year, including the momentous ‘All Rembrandts in the Rijksmuseum’ until 10 June and the Baroque exhibition ‘Rembrandt-Velázquez’ at the Rijksmuseum later on this year. Closer to home, a future exhibition at the Holburne Museum is set to showcase a selection of Rembrandt prints, among them his celebrated works from Oxford’s Ashmolean Museum, which holds an astonishing collection of more than 200 examples of the artist’s prints. Dulwich Picture Gallery aims to rejuvenate Rembrandt in a modern light through its highly anticipated exhibition, ‘Rembrandt’s Light’, which features cinematographer Peter Suschitzky’s innovative perspectives on the visual storytelling in 35 of Rembrandt’s works. With modern technology and art working hand in hand, we can be optimistic that Rembrandt’s legacy may continue for centuries yet.

Image credit: Jan Arkesteijn