Tag Archives: authentication

Damage-free art authentication and spatially offset Raman spectroscopy (SORS)

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In a world where people will shell out millions of dollars for a single painting, art authentication of some kind is mandatory from a buyer’s perspective while sellers might be a little more reluctant. Reliance on experts who have an intimate familiarity with an artist’s body of work, personal and professional history, as well as, the historical period in which the work was created is the norm. Technological means are not necessarily as heavily employed as one might expect. Given that most technical analyses require damage of some kind, no matter how miniscule, some reluctance is understandable.

A May 29, 2014 news item on phys.org describes a new, damage-free, art conservation and restoration process (which could easily be used for authentication purposes),

UK scientists, working on an international project to conserve precious works of art, have found a new way to analyse paintings without having to remove even a tiny speck of the paint to inspect the layers below.

Using laser spectroscopy, a method that uses light to probe under the surface of an object, the international team has developed a new, non-invasive way to identify the chemical content of the paint layers present.

This new technique will reduce the risk of damage to precious paintings, often worth thousands or even millions of pounds, when conservation and restoration work is being carried out.

Using laser spectroscopy, a method that uses light to probe under the surface of an object, the international team has developed a new, non-invasive way to identify the chemical content of the paint layers present.

This new technique will reduce the risk of damage to precious paintings, often worth thousands or even millions of pounds, when conservation and restoration work is being carried out.

Read more at: http://phys.org/news/2014-05-lasers-analyse-priceless-art.html#jCp

As noted in a March 24, 2014 posting about using surface-enhanced Raman spectroscopy (SERS) to determine the characteristics of red pigment in a Renoir painting, restoration, authentication, and conservation are all linked once researchers start a technical examination,

This next item is about forgery detection. A March 5, 2014 news release on EurekAlert describes the latest developments,

Gallery owners, private collectors, conservators, museums and art dealers face many problems in protecting and evaluating their collections such as determining origin, authenticity and discovery of forgery, as well as conservation issues. Today these problems are more accurately addressed through the application of modern, non-destructive, “hi-tech” techniques.

Getting back to this new technique, a May 28, 2014 Science and Technology Facilities Council news release, which originated the news item, provides information about the various agencies involved with this work and offers some technical detail about the new technique,

The new approach is derived from a technique called Spatially Offset Raman Spectroscopy (SORS). It was originally developed by UK researchers at the Science and Technology Research Council’s (STFC) Central Laser Facility within the Research Complex at Harwell. Now they have joined forces with researchers from the Institute for the Conservation and Promotion of Cultural Heritage (ICVBC), part of Italy’s National Research Council (CNR) to adapt this technology to test paintings without having to destroy any part of them.

The SORS technique involves shining the laser light onto an opaque object. A small number of photons (light ‘particles’) will scatter back, changing colour according to the different paint components they represent, and allowing the scientists to analyse the chemical composition in depth.

Professor Pavel Matousek, from STFC’s Central Laser Facility, explained. “Building on our earlier SORS research, we’ve transformed the method to allow us to probe the painted layers for the first time,” he said. “We’ve called it Micro-SORS because we can analyse the layers at the micrometer scale, rather than the usual millimetre scale”.

For comparison of scale, a human hair is about 100 micrometers wide.

Dr Claudia Conti, a scientist at the ICVBC in Italy, said, “When I heard about the potential of SORS and how it could be applied, I realised the huge contribution this method of analysis could bring to the conservation of artworks.”

The research team tested the Micro-SORS method by collecting data from the light scattered across a surface of painted layers, artificially prepared to mimic a real painting. They isolated the light signals of the individual paint layers, enabling them to assess the chemical make-up of each layer.

The next step in the team’s research is to optimise the sensitivity and depth of penetration, and apply the technique to real artwork.

SORS has been used in other applications, from the news release,

The original SORS technique has already been applied to a number of problems, including non-invasive breast cancer diagnosis and bone disease diagnosis.The Science and Technology Facilities Council (STFC) has also launched a spin-out company, Cobalt Light Systems, which uses the SORS technology and has recently developed products for scanning liquids in unopened bottles for airport security, and in pharmaceutical quality control.

Here’s a link to and a citation for the research paper,

Subsurface Raman Analysis of Thin Painted Layers by Claudia Conti, Chiara Colombo, Marco Realini, Giuseppe Zerbi, and Pavel Matousek. Applied Spectroscopy, Volume 68, Number 6, June 2014, pp. 686-691(6) doi.org/10.1366/13-07376 Available online via Ingentaconnect

This article is open access.

Authenticating chocolate and a bit about coffee

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Apparently, not all premium chocolate is actually premium, like wine, expensive, premium product can be mixed with a more common variety to be sold at the higher, premium price.  Now, scientists in a collaboration which spans the US, China, and Trinidad and Tobago have found a way to authenticate premium chocolate according to a Jan. 15, 2014 news release on EurekAlert,

For some people, nothing can top a morsel of luxuriously rich, premium chocolate. But until now, other than depending on their taste buds, chocolate connoisseurs had no way of knowing whether they were getting what they paid for. In ACS’ Journal of Agricultural and Food Chemistry, scientists are reporting, for the first time, a method to authenticate the varietal purity and origin of cacao beans, the source of chocolate’s main ingredient, cocoa.

Dapeng Zhang and colleagues note that lower-quality cacao beans often get mixed in with premium varieties on their way to becoming chocolate bars, truffles, sauces and liqueurs. But the stakes for policing the chocolate industry are high. It’s a multi-billion dollar global enterprise, and in some places, it’s as much art as business. There’s also a conservation angle to knowing whether products are truly what confectioners claim them to be. The ability to authenticate premium and rare varieties would encourage growers to maintain cacao biodiversity rather than depend on the most abundant and easiest to grow trees. Researchers have found ways to verify through genetic testing the authenticity of many other crops, including cereals, fruits, olives, tea and coffee, but those methods aren’t suitable for cacao beans. Zhang’s team wanted to address this challenge.

Applying the most recent developments in cacao genomics, they were able to identify a small set of DNA markers called SNPs (pronounced “snips”) that make up unique fingerprints of different cacao species. The technique works on single cacao beans and can be scaled up to handle large samples quickly. “To our knowledge, this is the first authentication study in cacao using molecular markers,” the researchers state.

Here’s an image, provided by the researchers, illustrating their work,

Courtesy American Chemical Society [downloaded from http://pubs.acs.org/doi/abs/10.1021/jf404402v]

Courtesy American Chemical Society [downloaded from http://pubs.acs.org/doi/abs/10.1021/jf404402v]

Here’s a link to and a citation for the paper,

Accurate Determination of Genetic Identity for a Single Cacao Bean, Using Molecular Markers with a Nanofluidic System, Ensures Cocoa Authentication by Wanping Fang, Lyndel W. Meinhardt, Sue Mischke, Cláudia M. Bellato, Lambert Motilal, and Dapeng Zhang. J. Agric. Food Chem., 2014, 62 (2), pp 481–487 DOI: 10.1021/jf404402v Publication Date (Web): December 19, 2013
Copyright © 2013 American Chemical Society

This story reminded me that coffee too is sold at premium prices. Billed as the most expensive coffee in the world, Kopi Luwak, is harvested, so they say, from civet excrement and I have to wonder how anyone could authenticate that a bean had actually passed through a civet’s gastrointestinal tract and out the other end. I’ve also wondered how the practice of plucking coffee beans from civet excrement started (from the Kopi Luwak Wikipedia essay; Note: Links have been removed) here’s an answer to the second question,

The origin of kopi luwak is closely connected with the history of coffee production in Indonesia. In the early 18th century the Dutch established the cash-crop coffee plantations in their colony in the Dutch East Indies islands of Java and Sumatra, including Arabica coffee introduced from Yemen. During the era of Cultuurstelsel (1830—1870), the Dutch prohibited the native farmers and plantation workers from picking coffee fruits for their own use. Still, the native farmers wanted to have a taste of the famed coffee beverage. Soon, the natives learned that certain species of musang or luwak (Asian Palm Civet) consumed the coffee fruits, yet they left the coffee seeds undigested in their droppings. The natives collected these luwaks’ coffee seed droppings, then cleaned, roasted and ground them to make their own coffee beverage.[11] The fame of aromatic civet coffee spread from locals to Dutch plantation owners and soon became their favourite, yet because of its rarity and unusual process, the civet coffee was expensive even during the colonial era.[citation needed]

I guess that in the future when you eat premium chocolate you can be sure that you’ve gotten what you paid for. As for coffee, I’m sure that industry is working on its authentication processes too and in the meantime, you’ll have to rely on your palate.