Issue 6 RSC. March 2014
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IONIC Issue 6 RSC - MESSAGE FROM THE EDITOR
Message from the editor Ionic Magazine 03.14 Issue 6 sees Ionic Magazine proudly collaborate with the Royal Society of Chemistry as part of their 2014 theme of Chemistry and Art. The Royal Society of Chemistry has recently published about breakthroughs sitting at the intersection of Science, Culture, History and Art. In this special edition, we showcase just a few of these. Read about advances in chemical analysis tools used in investigating paint binders, pigments and behavioural patterns of prehistoric man, in an effort to understand, conserve and restore artistic treasures that shape our cultural history. As always, glance over from the science to see our artists refract the research through a kaleidoscope of imagination and creativity. Chemistry and Art, meet Ionic.
Yalda Javadi Ph.D. Editor
IONIC Issue 6 RSC - CONTENTS
Contents Fifty shades of green
Looking beyond the surreal
By Yalda Javadi - Illustration by Paul Jackson
By Jenni Lacey - Illustration by Tom Lacey
State-of-the-art
Keeping the Dead Sea Scrolls Alive
By Xavier Roeseler - Illustration by Najwa Mahayni
By Megan Lightfoot - Illustration by Jon Heras
Will there be blood?
Fishing for Isinglass
By Hayley Bennett - Illustration by Caroline Grainger
By Jennie Garbutt - Illustration by Angie Brown
Fingerprints of the Past
The Mysterious Chemical Legend of the Dead Sea Scrolls
By Rakesh Parmar - Illustration by Megan Lightfoot
By Carl Spickett - Illustration by Joanna Senez
Sunflowers, a yellow house and a starry night By Lux Fatimathas - Illustration by Anthony Lewis
Fifty shades of green By Yalda Javadi - https://twitter.com/yjavadi
W
hen you think of the colour green what springs to mind? Do you think of fields, nature, or environmental movements? Perhaps, you associate green with certain cultures, celebrations, even religions? Maybe you have an emotional association, having been green with envy on occasions? Quite simply, whether symbolic or literal, green is everywhere and as such has been well documented throughout history within art and manuscript illumination. Now, as part of a broader research project that aims to shed light on the historical, art-historical, social and political context in which manuscripts were commissioned, executed and used, researchers from the Fitzwilliam Museum and the University of Cambridge have began their exploration into the colour green. Dr Paola Ricciardi and her team focused on 13th to 16th century French illuminated manuscripts – a time where Paris was becoming one of the most densely populated cities in Europe and the number of artisans was multiplying rapidly. On the lookout for greencoloured areas within these manuscripts, the team undertook analytical investigations using visible and near-infrared fibre optic reflectance spectroscopy (FORS). With valuable and fragile manuscripts under investigation, a non-invasive approach is key. In this respect, FORS fit the bill: it applied no physical strain to the manuscript. What’s more, the equipment was portable and provided quick results, yielding information on the chemical structure and the presence of certain organic or inorganic materials within the pigments. Interested in getting a sense of which green pigments were preferred by French illuminators during the medieval and Renaissance period, the team analysed
treatises, which alongside containing in-depth written instructions on manuscript illumination, contained the colour green. Their results revealed that throughout the Middle Ages and until the 18th century, Western European illuminators were limited to the range of green material they used. Essentially, verdigris – the green obtained from copper containing compounds – was clearly the pigment of choice in the 13th and 14th century treatises, albeit at times was mixed with plant extracts to modify the colour. The study also revealed that in the 14th and 15th century treatises, the green palatte expanded to include green earth, malachite, sap green and other plant juices to its list, which could be potentially ground together with azurite to obtain ‘a very lovely green.’ This contextualised study has laid the groundwork for future investigations of its kind. Scientists are now interested in extending their analysis to include a complete characterisation of mixtures, from yellows and blues, and organic glazes, as they look out for trends that emerge in the use of different pigments by different artists or workshops, in different periods of time and geographical areas.
Ricciardi P, Pallipurath A, Rose K. Analytical Methods. 2013,5, 3819-3824. doi: 10.1039/c3ay40530c. ‘It’s not easy being green’: a spectroscopic study of green pigments used in illuminated manuscripts
By Paul Jackson
https://www.facebook.com/pauljacksonartist
IONIC Issue 6 RSC - Fifty shades of green
State-of-the-art By Xavier Roeseler - http://www.flickr.com/photos/xavier_roeseler/
H
ave you ever thought about the challenges faced by art conservation scientists? No, neither had I. But in order to better understand art, what it’s made of and how it’s conserved or restored, efforts have to be placed in analysing each and every stroke, pigment and material used. However, an avid Da Vinci expert cannot simply ask the Louvre to take a sample from the Mona Lisa because they want to better understand what pigment and paint binder is used that differentiates the pale aspect of her upper breasts from the darker hues of her lower neck. This is where a type of chemical imaging technique called near-infrared reflectance imaging spectroscopy comes in. One of its main advantages is that it is non-destructive and non-invasive; it is an in situ analysis tool, which means you do not need to take a sample of the matter you wish to analyse. As such, this technique is fast becoming an important tool in cultural heritage science. A paper published last summer showed the accuracy and relevance of using near-infrared reflectance imaging spectroscopy in the field of conservation science. Early Renaissance paintings were analysed and scientists discovered that the painter, Cosimo Tura, had used two different paint binders – animal skin glue and egg yolk tempera – for different parts of the paintings. Animal skin glue binder mapped to blue areas of the painting whereas the binder in the red and brown parts corresponded to the egg yolk tempera. In addition, they noted that the binders co-localised in particular parts of the painting, namely the faces, displaying the complex layering of materials to render the faces.
Much like any spectroscopic method, near-infrared reflectance imaging spectroscopy studies the interaction between matter and radiated energy, in this case a near-infrared beam. The method relies on the fact that chemical bonds within molecules, such as O-H, N-H and C-H, absorb energy at a particular wavelength within the near-infrared spectrum and start to ‘vibrate’ in a process known as molecular vibration – some stretch, some scissor and others rock. Since it is known how particular chemical bonds within types of molecules vibrate, the measurement can identify what types of molecules are in the sample, and in what quantity – detailing the materials used. This story is a beautiful example of the interdisciplinary nature of science today. On the one hand, we have chemical engineers developing intricate techniques for identifying and mapping organic components, while on the other, we have cultural heritage scientists applying these methods to restore and better understand how paintings several hundred years old came about.
Dooley KA, Lomax S, Zeibel JG, Miliani C, Ricciardi P, Hoenigswald A, Loew M, Delaney JK. Analyst. 2013 Sep 7;138(17):4838-48. doi: 10.1039/ c3an00926b. Mapping of egg yolk and animal skin glue paint binders in Early Renaissance paintings using near infrared reflectance imaging spectroscopy.
By Najwa Mahayni
http://najwa.edublogs.org/
IONIC Issue 6 RSC - state-of-the-art
IONIC Issue 6 RSC - Will there be blood?
Will there be blood? By Hayley Bennett - http://uk.linkedin.com/pub/hayley-bennett/1b/288/539
C
hemists have teamed up with conservationists at the Detroit Institute of the Arts and uncovered the composition of an unusual ceremonial mask.This story of discovery brings together the ritual dances of the Bamana people of Mali and the latest techniques in mass spectrometry. Striking and somewhat terrifying, the Komo mask is a Smörgåsbord of strange materials, including horns and quills, fur and feathers – based upon skulls and wrapped with cloths. But that’s not all; encrusted on this mask is a mud-like material of unknown origin. Given that the Banama people were known to use blood in their rituals to symbolize power, museum specialists naturally wondered: Could the mask’s encrustation contain blood?
To answer this, chemists initially bombarded a sample from the mask with X-rays and found an abundance of iron, which was suggestive of blood. Next, using mass spectrometry, the chemists directly looked for the major protein found in blood - haemoglobin. Mass spectrometry works by first, destroying and breaking down the sample into tiny pieces of molecules or atoms. These make charged ions, which can be separated out depending on their size and charge. Every single protein has a unique signature; so mass spectrometry stands as a very powerful method in identifying unknown samples. As the mask was probably 100 to 200 years old, it was unknown how the mass spectrometry signature of haemoglobin would change over time. Before destroying the precious sample from the mask the mass spectrometry approach had to be tested. The chemists were able to draw on another resource at the Eastern Michigan University; a long-term study of the binding agents used in rock paintings. Slides
with drops of blood, bone marrow and egg made ten years ago, were stored either in the lab, outside and covered, or left outside completely exposed to the weather. On these samples, mass spectrometry revealed a distinct peak in the blood samples, which was missing from the other samples. This peak appeared even in blood samples that had been left unprotected outdoors. Satisfied that their method could detect ‘old’ blood, the chemists tested a small flake of material from the Komo mask. The test only took two minutes to run and the result was very clear – the covering of the mask does indeed contain blood. By working together on this case museum specialists and chemists have shown how contemporary chemistry can be used to give new insight into cultural rituals that are centuries old.
Fraser D, DeRoo CS, Cody RB, Armitage RA. Analyst. 2013 Aug 21;138(16):4470-4. doi: 10.1039/c3an00633f. Characterization of blood in an encrustation on an African mask: spectroscopic and direct analysis in real time mass spectrometric identification of haem.
By Caroline Grainger
https://www.facebook.com/CarolineTheChemistArtwork
IONIC Issue 6 RSC - Fingerprints of the past
Fingerprints of the Past By Rakesh Parmar - http://uk.linkedin.com/in/rakeshparmar1
T
he image of a prehistoric man wearing animal skin hunting for wild animals is one that is familiar to us. What might be less familiar is the ‘waste not want not’ attitude they had towards the remains of a days kill. Being ever resourceful, kill remains were transformed into artwork, clothing, religious objects, tools and toys. Now, scientists have developed a technique that can take a detailed look at these objects and provide insight into the lifestyles and evolution of craft techniques, as well as information on the planet’s biodiversity, making them not just cultural artefacts, but equally important natural history artefacts too. The technique, known as Peptide Mass Fingerprinting (PMF), identifies collagen-based materials, such as mammalian guts and sinew, commonly used in the manufacture of such prehistoric objects. While, traditional methods failed to pinpoint the source of the material and required specialists to carry out the analysis, PMF can be conducted by a non-specialist, and provides the level accuracy and specificity required to identify the animal source of a material down to a specific species. PMF begins with enzymatic breakdown of the sample, cutting long protein chains into small identifiable chunks (peptides). The peptide mixture forms a unique ‘fingerprint’, from which the species of origin can be determined from peptide-marker databases. Using the method and a recently constructed seamammal database, scientists were able to identify two historic Alaskan kayaks: a Yup’ik vessel from the mid-nineteenth century and an Alutiiq vessel from the late nineteenth century. Kayaks were originally used as a sleek hunting vessel, constructed from animal skins stretching over wooden or whalebone
frames. Stitching and skin samples were collected and analysed. The skin covering the Yup’ik kayak was found to be that of a bearded earless seal, while the stitching was made from caribou. The skin of the Alutiiq kayak was also found to be that of an earless seal, and the stitching was from a humpback whale. In addition to the kayaks, the team also analysed nearly 100 samples from 30 Alaskan native objects. In a relatively short period of time, they were able to identify objects of previously unknown origin, and also corrected wrongly assigned objects. PMF is able to handle a considerably large amount of data and as such gives researchers, artisans and cultural groups valuable information into the biodiversity present at that time. The hope is that this in turn will lead to a better understanding of the preservation needs of historic and cultural artefacts for generations to come. Kirby DP, Buckley M, Promise E, Trauger SA, Holdcraft TR. Analyst. 2013 Sep 7;138(17):4849-58. doi: 10.1039/c3an00925d. Identification of collagen-based materials in cultural heritage. Modern Analytical Methods in Art and Archaeology, M.P. Colombini and F. Moodugno, John Wiley & Sons, Inc., New York, 2009.
By Megan Lightfoot
mvlightfoot@gmail.com
IONIC Issue 6 RSC - looking beyond the surreal
Looking beyond the surreal
By Tom Lacey
By Jenni Lacey - https://twitter.com/Jenni_Lacey
M
any artists may dream that their work will live on forever, but few would suspect their work would be at the centre of pioneering efforts to improve art management in the 21st century. This, however, is exactly what has happened for surrealist painter, Salvador Dalí. A recent study, published in the Royal Society of Chemistry’s Journal Analytical Methods, describes a cross-disciplinary approach by scientists, curators and art conservationists to explore non-destructive ways of assessing the composition and integrity of precious canvases. This will help curators to find out whether a canvas or portrait is in a suitable condition to be transported for exhibition. It seems appropriate that the subject of this study was Dalí who had a keen curiosity in scientific matters and often explored these themes in his work. Typically, studies that address the question of art preservation focus on the characteristics within the paint. This latest study, quite uniquely, seeks to describe the condition of Dalí’s canvases, which form the very foundation of the painting. The study used near infrared spectroscopy (NIR) and sophisticated data analysis to categorise 12 Dalí paintings, determining if they were fit for handling and travel. NIR analysis provides information on the chemical composition of a sample based on its absorption of radiation at different frequencies. This effectively tells researchers about the chemical makeup of the canvas fibres without touching them and is often described as providing a chemical fingerprint.
The team of researchers first used a collection of sacrificial historic canvas samples to create reference data against which the Dalí paintings could then be compared. Chemical and NIR analysis was carried out on 199 historical canvases that were from the same provenance as the Dalí paintings. The researchers recorded the pH level, degree to which fibres had been weakened by acidity, fibre type and finally NIR data. This body of information was then used to build a statistical model that allowed them to predict canvas properties without chemical analysis. The Dalí paintings were then examined using just NIR methods. These can be performed in situ and without the constraints of a laboratory setting. The researchers were able to compare the NIR results from the reference data to that of Dalí portraits and reliably infer the canvas material, pH and degree to which fibres had been weakened, without carrying out any destructive testing. The final stage of the study was to classify the quantitative data into meaningful categories to determine if the Dalí paintings were fit for transportation and then hanging. Only one canvas of the 12 was deemed to be very fragile and moving was not advised. This study represents a repeatable framework for the examination of precious art, demonstrating the exceptional scope there is for scientific and statistical analysis to play an important role in art conservation. Studies such as these will help define ways of protecting valuable works of art and possibly increase the life of iconic pieces, helping immortalise artists such as Dalí, as well as their creations.
Oriola, M; Mozir, A; Garside, P; Campo, G; Nualart-Torroja, A; Civil, I; Odlyha, M; Cassar, M; Strlic, M. Analytical Methods. 6 (1) 86 - 96. doi: 10.1039/c3ay41094c. Looking beneath Dali’s paint: non-destructive canvas analysis.
IONIC Issue 6 RSC - Keeping the dead sea scrolls alive
Keeping the Dead Sea Scrolls Alive By Jon Heras
By Megan Lightfoot - mvlightfoot@gmail.com
I
n 1947, a Bedouin shepherd entered a deserted cave in the vicinity of Qumran, near the Dead Sea, not knowing that he was about to make one of the most important religious discoveries in history. Inside the cave he found a nest of jars containing mysterious rolls of parchment. As he unravelled the ancient manuscripts he was the first person in centuries to witness the sacred writing hidden within. He had discovered the first of the Dead Sea Scrolls. In the following nine years, over 900 fragments of ancient Jewish texts were found in eleven caves throughout the Qumran area. Written over 2000 years ago on parchment, papyrus and leather, the scrolls are of great cultural and historical significance; they contain the oldest known surviving manuscripts of books in the Hebrew Bible. While some are in good condition, other scrolls are badly damaged. In order to preserve these important texts, a reliable and accurate method is needed to assess their condition and monitor any further deterioration. Previous methods used to examine the current state of the Dead Sea Scrolls left analysts with a difficult choice: getting accurate levels of degradation but destroying a small sample of the scroll; or leaving the scroll intact at the expense of inaccurate and unreliable results. Enter the method that saves analysts from this painful decision: Polarised Raman Spectroscopy (PRS), a powerful yet non-invasive, non-destructive technique, able to give accurate results while leaving the artefact intact. PRS has been used by one group of researchers to reveal new insights into the condition of a significant scroll, the Temple Scroll.
Spanning eight metres long the Temple Scroll is of great importance as it contains text previously unknown. The research group led by Dr Admir Masic used PRS to quantify the amount of degradation observed in the scroll parchment. Parchment is made from animal skin; a major component of skin is collagen. In freshly prepared parchment, collagen fibres are organised in neat chains. As the parchment ages, collagen fibres degrade and change from neat rows into a disorganised mess in a process known as gelatinisation. In short, the messier the collagen the more damaged the scroll. The group developed a method to quantify the level of degradation by using PRS to measure the amount of gelatinisation in different sections of the Temple Scroll. The resulting analysis showed that the level of gelatinisation varied across the scroll, revealing some sections of parchment to be in far better condition than previously thought. Areas in the centre of the scroll were well preserved; foremost, because the outer layers protected this central region when the manuscript was rolled up thousands of years ago. This new insight should help preserve the Dead Sea Scrolls for many more years to come. As collagen is present in many natural materials, the team also believe this method can be used to monitor the condition of wool, silk and hair artefacts. Therefore, PRS should prove a powerful tool for preserving our rich cultural history for future generations. http://www.deadseascrolls.org.il/learn-about-the-scrolls/introduction, Accessed 24 November 2013. Sch端tz, R., Bertinetti, L., Rabin, I., Fratzl, P., and Masic, A., Analyst. 138, 5594-5599, 2013. doi: 10.1039/c3an00609c. Quantifying degradation of collagen in ancient manuscripts: the case of the Dead Sea Temple scroll
http://www.e-nox.net/
IONIC Issue 6 RSC - fishing for isinglass
Fishing for Isinglass By Jennie Garbutt - http://jenniegarbutt.wordpress.com/
“
Art is science made clear” according to American playwright Wilson Mizner. Recent research published in Analyst would beg to differ. Using science (or specifically mass spectrometry) to make art clear, Sophie Dallongeville and colleagues successfully identified the biological origins of a glue used to glaze a sculpted Baroque angel.
The angel they studied is one of a pair flanking a 17th century altarpiece in the church of St. Michael of Mondsee in Austria. At first glance, the worshipper would have been struck by the heavenly glow of the angels, achieved by the use of an unusual embellishing technique; the application of green lacquer to a layer of silver leaf. The angel’s glow also depends on the glue used to stick the lacquer to the silver leaf; art historians and restorers are keen to identify its biological origins. Ancient texts claim that it is isinglass, a glue made from the swim bladder of a sturgeon, but this has never been confirmed. Dallongeville and colleagues set out to identify the glue. They expected it to be mostly composed of proteins and so stained a small sample of the angel with a molecule that, when bound to a protein, glows under UV light. This confirmed the presence of a thin protein-containing layer between the silver leaf and green lacquer. To identify the animal origins of the proteins the researchers used mass spectrometry. The technique works by characterising the sequence, or order, of the building blocks – amino acids - that make up a protein. Because fish proteins will have a unique amino acid sequence that differ from other animal proteins, this technique can be used to determine the
biological origin of mystery samples. The researchers looked for matches to the glue amino acid sequence in a database of known sequences and got several hits: all segments belonging to the fish version of collagen (a major component of nails, skin and bones). Unfortunatley however, the researchers were unable to tell which species of fish the collagen came from because of a lack of fish collagen sequences in the database. The presence of fish collagen in the material proved the ancient texts right - a glue containing fish was used to embellish the angel. Even though we remain ignorant of whether it was actually isinglass that was used, knowing that the glue was made of fish proteins should help restorers to carefully conserve and restore the angel. This research paves the way for mass spectrometry to identify biological material in other works of art. Because the authors used only a tiny amount of starting material, they showed that this technique could be minimally destructive. Hopefully mass spectrometry will continue to be used to aid the restoration of ancient artworks and continue to prove that sometimes science really can make art clear. Dallongeville S, Richter M, Schäfer S, Kühlenthal M, Garnier N, Rolando C, Tokarski C. Analyst. 2013 Sep 21;138(18):5357-64. doi: 10.1039/ c3an00786c. Proteomics applied to the authentication of fish glue: application to a 17th century artwork sample.
By Angie Brown
http://www.galacticbloom.com/
IONIC Issue 6 RSC - The mysterious chemical legend of the dead sea scrolls
The Mysterious Chemical Legend of the Dead Sea Scrolls
By Joanna Senez
By Carl Spickett
T
he story of the Dead Sea Scrolls rivals that of comic book adventures. While in search of an errant goat, a Bedouin boy found a cave in the Judean Desert. Inside were ancient scroll writings, remarkably intact, awarding insight into the ancient Jewish people that populated the region. With the authenticity of the scrolls confirmed in the late 1940s, the race was on to uncover further ancient writings in and around the first cave. Fifteen years and many caves later, archaeologists had located thousands of fragments at various locations. At the same time however, the Bedouin, with a wealth of local knowledge and an eye for profit, had located a number of fragments themselves. In those exciting days of excavation and discovery, there were no clear records of the location of finds. Furthermore, excavated materials were mixed with others purchased from local tribes. Although fragments have been grouped together based upon their content and layout, up until now it has been impossible to prove their relationship. New research from Ira Rabin and colleagues from BAM Federal Institute for Materials Research and Testing in Berlin, highlights the use of sophisticated chemical spectroscopy methods to discover the origins of the writings. The technique can identify the chemical makeup of a material by looking at its unique energy fingerprint. This uses the relationship between a material and the energy spectrum it radiates under certain conditions to determine which chemicals are present. Crucially, modern spectroscopy methods allow this to be achieved non-invasively, helping preserve precious
ancient samples such as the scrolls. The researchers first measured the relative amounts of the chemicals bromine and chlorine found in Dead Sea water. From this reference they were able to identify where the water used to create the ink and prepare the parchment came from, giving a location for the writing place of the fragments. Storage contaminants found on the scrolls, presenting as localised, distinct patches on the surface, provided knowledge of the sediments present in the caves where the scrolls were kept. Some fragments also showed isolated spots of salt where the skins were cured for storage for later use. Sediments of stone were identified only on the surface and not in the parchment core indicating this was a surface contaminant. Surface mineral deposits were linked to those found in specific caves in the Judean Desert. Finally, parchments could be distinctly grouped into those with or without the preservative tannin. A clear fingerprint attributable to tannin was visible between an eastern darkly tanned product and a western lighter, non-tanned parchment. This finding is fascinating in that it showes that there existed two geographically distinct methods of manufacturing parchment. The key to the successful use of the technology in this study was the clever integration of different spectroscopic methods. This allowed the researchers to differentiate between chemicals used in production from contaminants, providing a wealth of knowledge from which it is now possible to unravel some of the mysteries of these ancient documents.
Rabin I, Hahn O. Analytical Methods. 2013,5, 4648-4654 doi: 10.1039/C3AY41076e. Characterization of the Dead Sea Scrolls by advanced analytical techniques.
IONIC Issue 6 RSC - sunflowers, a yellow house and a starry night
Sunflowers, a yellow house and a starry night
By Anthony Lewis
By Lux Fatimathas - https://www.facebook.com/l.fatimathas
“
These colours give me extraordinary exaltation. I have no thought of fatigue; I shall do another picture this very night”. And so he did, time and time again. The famously mad Vincent Van Gogh produced many great works of art. Sunflowers, The Yellow House and even A Starry Night all bring to life Van Gogh’s particular love of the colour yellow. Some theorists even suggest that Van Gogh truly did see the world in shades of yellow – a side effect of remedies such as digitalis and absinthe, used to counteract his seizures. Whatever the reason, Van Gogh adorned his paintings with every kind of yellow to hand: from Naples yellow and ochre to lemon and chrome yellow. These splashes of colour were created from a range of synthetic and organic yellow dyes, each bringing their own ‘origin story’ to the canvas. Art historians seek to uncover the composite dyes used to create a particular colour so they can better date a piece of art, interpret its meaning, preserve and restore it. An entire field of research has consequently grown up around identifying the organic dyes a long-dead painter once used. The latest effort is a twist to a technique called Raman spectroscopy. Raman spectroscopy shines a beam of light - somewhere between ultraviolet and near infrared - onto a paint sample. Each component with the paint scatters the light differently, creating a unique ‘spectral fingerprint’. This fingerprint can then be used to identify the mystery components against a catalogue of fingerprints of known compounds. The problem with regular Raman spectroscopy however is its power. More specifically, the beam of light shone onto the paint sample is powerful enough to degrade the very dye it is trying to detect. Raman
http://www.anthony-lewis.com/
version two – or rather Surface-enhanced Raman spectroscopy (SERS) - presents a way to overcome this. SERS shows much greater sensitivity than regular Raman spectroscopy, and can therefore be used to identify mystery components with less destruction of the paint sample. The physics behind exactly how SERS achieves this is still a topic for debate. The trick lies in how the sample is presented. In SERS, unlike regular Raman spectroscopy, the sample is adsorbed onto a metal surface – this seemingly simple adjustment is what enhances its sensitivity. All of this sounds great in theory but what about in practice? Pretreating a drop of oil paint with a concoction of acids and alcohols, before subjecting it to SERS, has already proven successful in detecting indigo and Prussian blues in oil paint. However as Van Gogh once said “There is no blue without yellow and without orange.” The vivid landscape of yellow oil paints had been largely unexplored by SERS – that is until now. A team of US researchers have focused their efforts on producing clean, accurate spectral fingerprints of a range of natural yellow dyes. They then tested the usefulness of their technique by measuring the same spectra in the corresponding oil paints created from these dyes. The dyes tested fell into two categories: organic dyes and lake pigments. The latter term, although suggesting a dye sourced from the depths of a body of water somewhere, actually refers to a dye bound to substance such as a metallic salt in order to create a thick, glossy paste. ‘Lake’ in this case actually refers to the word ‘lac’ meaning a resin-like secretion.
In order to successfully identify the lake pigments Still de Grain and Reseda Lake within microscopic amounts of their corresponding oil paints, the samples first had to be pretreated with a tiny amount of hydrochloric acid and methanol. Following this simple pretreatment, the spectra of these dyes were clearly detected using SERS. When it came to oil paints generated from the organic dyes turmeric, old fustic and Buckthorn berries, this pretreatment proved unneces sary – SERS alone was successful in detecting their unique spectra.
For the very first time, SERS has been shown to be an eagle-eyed sleuth when it comes to detecting yellow dyes in oil paints. With the trials and tests now complete, its time to put SERS into the field and see what historical insights this new player can bring to the yellow world of art. Mayhew HE, Fabian DM, Svoboda SA, Wustholz KL. Analyst. 2013 Aug 21;138(16):4493-9. doi: 10.1039/c3an00611e. Surface-enhanced Raman spectroscopy studies of yellow organic dyestuffs and lake pigments in oil paint.
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