Our Illuminating Objects project for 2017 is now underway. In a series of blog posts postgraduate intern Natasha Gertler will share her discoveries as she chooses and researches the next Illuminating Object.
With an academic background in physics and an unwavering curiosity for crystals since, well, forever, it was only natural for me to choose the intricate frame bearing the double sided Aertsen painting for my ‘Illuminating Objects’ internship. Acquired by Count Seilern in 1969 from Alessandro Orso in Milan, the frame is beautifully inlaid in pietra dura with a multitude of semi-precious stones.
Or so we thought…
Upon initial inspection (which, by the way, was true love at first sight) and discussion with Sacha, Curator of Sculpture and Decorative Arts with whom I am working on this project, and Graeme, Chief Conservator, we had speculations of the material composition of the frame; that the central upper disc showing concentric red and white rings was pink agate, the two purple columns either side of the painting were amethyst and the several rich blue segments, lapis lazuli. But, as with most scientific investigations, things are not often as they seem and we needed to perform analytical experimentation to be sure.
In order to gain some insight into the constituent elements of the stones, we ventured down to the conservation laboratory of the Courtauld to use the X-ray Fluorescence (XRF) facilities, with the expert guidance of Professor Aviva Burnstock and Silvia Amato.
Having used spectroscopy many times in my undergraduate physics experiments (albeit on far less beautiful objects!) I felt quite at home and even a little nostalgic in the Courtauld’s lab. XRF works by shooting X-rays at a sample and then analysing the energies of the X-rays reflected back to the detector, which are characteristic to each individual element.
As expected, areas of red colour showed a dominance of iron (Fe) in their spectrum, and the dark blue areas exhibited the presence of Calcium (Ca) which is typical of lapis lazuli. However, many different stones as well as manmade materials also have several elements in common with each other. For example silicon (Si) is present in both agate and glass. Therefore, XRF cannot be used as a conclusive method of material identification, but rather as a further analytical tool.
Red, round element in the central upper area. Presence of silicon and iron.
Central blue segment below the painting. Presence of calcium.
Purple element, middle horizontal element below columns. Presence of silicon.
For that reason, we turned to visual analysis instead. Dr. Emma Passmore, a senior teaching fellow in Earth Sciences at Imperial College London with experience in object analysis for the British Museum, kindly came to the Courtauld’s depot to help us identify these mystery materials. She agreed with our initial theories and added that the mirroring light blue elements on the lower panel were also agate.
However, she also suggested that some of the segments might not be semi-precious stones at all, but rather synthetic imitations. These included for example the panels that look like tigers eye and the red ovals at the very bottom, as well the orange and purple coloured banners across of the top and bottom of the painting, respectively.
Professional geologists identify stones by smashing and slicing them to make slides which they can then analyse under a microscope to a very high degree of accuracy. However, in the case of historically important and valuable objects such as this unique frame, this of course is not an option and alternative, non-intrusive methods must be used instead.
Will we ever be able to know the materials present in the frame with absolute certainty? Perhaps. And so the quest for identity continues…
Illuminating Objects is a series of displays that shines a light on unexpected objects from The Courtauld’s decorative arts and sculpture collection.