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Science meets Art: Investigating pigments in art and archaeology
By ucftafe, on 4 July 2011
The Lunch Hour Lecture series has been on tour for the last three weeks at the British Museum. Aptly enough, the last lecture of this ‘tour’ dealt with the meeting of two fields that sound very different, but that in reality can very much complement each other: science and art. As a PhD student at the Centre for Sustainable Heritage working in this very field I couldn’t miss it!
First the theory: In 1928, CV Raman, an Indian scientist, discovered that when light falls on an object most of it is scattered while keeping the original frequency of light falling on the material. However, some of the light also interacts with the molecules making up the material, in the process increasing or decreasing its energy. These interactions are highly specific to an individual molecule and can characterise a molecule quickly and uniquely. Raman Spectroscopy uses these phenomena to provide spectra of these side-bands, and hence, essentially, provide fingerprints of the molecules. This is the tool used most commonly to examine pigments.
Watch Professor Clark’s lecture at the British Museum (45 minutes)
Having explained the concepts behind the main technique he uses, Professor Clark then went on to provide examples of items he has studied in the past and what the conclusions of those studies were. He mentioned situations where identifying a pigment is important for purposes of restoration and conservation. He in fact discussed a painting where the areas of highlight on a hand actually appeared blacker, rather than whiter. A study of the pigment discovered that the original white pigment, lead carbonate, on exposure to sulfur dioxide (a pollutant), gave a black pigment, lead sulfide, leading to this unexpected appearance.
The examples that mostly intrigued me, however, were probably the ones where the authenticity of a work of art was in question. Professor Clark discussed a number of situations. In one case, rare postage stamps from Hawaii were identified as fake, as real stamps had the pigment ultramarine blue in the paper to make it appear whiter, while the fake ones didn’t. In another case, someone was trying to sell around 100 papyri for around £2 million each, but on even cursory examination he could identify that they were actually fake as they contained synthetic pigments that were not around during the time period they were supposedly produced. In another case, the papyrus was actually printed using an inkjet printer!
However, unfortunately, this technique cannot provide the answer to all questions! As Professor Clark explained, if you find a pigment in a work of art which should not be there, you can rule out the work of art immediately as either a fake or one that has been repainted. However, if you only find what you expect, that does not prove anything.
A very enlightening lecture, and one which clearly showed that, quoting Professor Robin Clark, “You admire it as a piece of art work [but] there is also excellent science”.
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Janet Ambers – British Museum Scientist, Radiography & Raman spectrometry, Department of Conservation & Scientific Research comments on the lunch hour lecture by Prof Robin Clark.
Science is playing an increasingly important part in our understanding of the past. This lavishly illustrated and wide ranging Lunch Hour Lecture by Professor Robin Clark, the Sir William Ramsay Professor Emeritus of Chemistry at UCL, concentrated on a very specific area of this field, the use of Raman spectroscopy to identify the pigments used in ancient and modern artworks, an application in which Professor Clark has been a pioneer.
The talk started with a clear and concise explanation of the Raman effect, not an easy thing to summarise in a few words, particularly for a general audience. Professor Clark then went on to show how this powerful method can be applied to conclusively identify the materials used to colour objects without the need to take samples or, in fact, for any contact with the surface of the object at all (frequently an essential requirement for an examination of works of art).
Professor Clark also spoke about his work on early manuscripts with particular emphasis on the appearance (or sometimes the non-appearance) of lazurite, the mineral which gives the rare semi-precious stone lapis lazuli its blue colour. Lazurite can be ground to produce a bright blue pigment which features in much early artwork, but not, as it turned out, in the Lindisfarne Gospels, one of the greatest treasures of the British Library. Since the only place that lapis could be obtained in the ancient world was from the Sar-e-Sang region of Afghanistan, the distribution of this pigment, once more expensive than gold, can tell us much about early trade.
A particularly entertaining section of the talk was devoted to an important use of Raman analysis within the art world; the identification of forgeries. In many cases the discovery of anachronous painting materials in an artwork will reveal a modern origin. Professor Clark’s examples ranged through some suspiciously bright ‘Ancient Egyptian’ papyri (with extremely optimistic owners), through works apparently by Vermeer and Inglès, to sets of potentially high value stamps. In some cases the forgers showed great skill with only slight slips in the chronology of the paints present giving them away. In others the makers showed rather less knowledge, with the finest example of this being the use of an ink jet printer.
Professor Clark also illustrated how pigments can change colour over time and just how much difference this can make to the appearance of paintings.
This was a stimulating and entertaining talk which clearly demonstrated the power of applying science to the humanities through a series of fascinating case studies.