foster+freeman BLOG
Forensic Multispectral Imaging in Fine Art and Cultural Heritage Applications
This month marked the 22nd Symposium for the Study of Underdrawing and Technology in Painting, with foster+freeman delighted to have a team of staff in attendance to present our unique Crime-lite AUTO and new VSC 900 to experts within the field, showcasing their forensic multispectral imaging capabilities in fine art and cultural heritage applications.
These products, from our market-leading VSC and Crime-lite ranges, offer Infrared, Visible and Ultraviolet multispectral imaging, empowering examiners to reveal hidden information, detect forgeries and better conserve our cultural heritage.
Read on as we make use of case studies to explore the value foster+freeman VSC and Crime-lite products offer in fine art and cultural heritage applications.
A book undergoes multispectral imaging analysis using a VSC 8000/HS workstation
foster+freeman VSC 900 and Crime-lite AUTO during a product demonstration at the symposium
The symposium brought together experts from leading organizations in the field in Leuven and Brussels for a three-day congress, organised by KU Leuven, Illuminare, UCLouvain, Musea Brugge, KIK-IRPA, KBR and M Leuven.
Providing a scientific forum for researchers in the field to share and discuss the latest technical studies in art history, this years event focussed on art from the Middle Ages and Early Modern period, exploring the applications of forensic multispectral imaging in art and cultural heritage.
The conference focussed particular attention on the technical considerations of examining art produced on varied substrates and in a wide range of media, including canvas, cartoons, drawings, panel paintings, painting on parchment, sketches, sketchbooks, manuscript illuminations, and prints.
You can find more information on the symposium here:
Technical Art Studies – 2024 I Leuven (technicalartstudies2024leuven.be)
Symposium XXIII for the Study of the Underdrawing and Technology in Painting | KIK-IRPA (kikirpa.be)
Key Products
for forensic multispectral imaging in art and cultural heritage
VSC Range
While our VSC range of multispectral illumination workstations has its roots in questioned document examination, often in immigration and law enforcement settings, it also represents a powerful tool in the hands of an art authenticator, researcher or conservator.
Found at border security points across the globe, VSC devices excel in the detailed examination of complex travel and identity documents. The same qualities that facilitate the successful forensic examination of a passport, for example, complete with myriad features invisible to the naked eye, naturally lend themselves to the detailed analysis of artworks and cultural artefacts, with the VSC range representing significant opportunities for forensic multispectral imaging in art and cultural heritage applications.
Crime-lite Range
We originally conceived the Crime-lite range of multispectral forensic light sources for use in law enforcement applications, as the name suggestions. However, like our VSC products, Crime-lites excel in wide-reaching applications beyond their original purposes.
Our versatile Crime-lite products, offering powerful and consistent multispectral illumination from portable and robust devices, are ideal for examining artworks and cultural artifacts. Importantly, Crime-lites prove effective not only in lab settings but also in-situ, making them the preferred choice when dealing with objects that may be too large or fragile to be moved practically.
Our Crime-lite AUTO combines this multispectral illumination with powerful imaging capabilities and built-in filters and pre-sets, allowing examiners to visualise and capture details otherwise hidden from the naked eye, on-site and with the agility of a standard digital SLR.
Background
Multispectral Imaging and Infrared Reflectography
Multispectral imaging refers to capturing images of a document under different illumination wavelengths across the electromagnetic spectrum (including UV, visible and Infrared light), which can then be analysed. One key technique used to examine artworks and manuscripts is Infrared reflectography. This technique is based on the ability of infrared light to penetrate layers of paint, paper and other materials that visible light cannot, allowing an examiner to see beneath the surface of a document and reveal otherwise hidden details. Different materials will also react differently under specific IR wavelengths, allowing them to be isolated from one another and analysed individually.
UNDERDRAWINGS
With specific reference to paintings, it is common practice for artists to make marks on the substrate before going on to cover these with the layers of paint which form the surface of the painting. These ‘underdrawings’ often act as a plan or sketch for the artist to follow, helping them to finalise the composition and other elements of the work. With individual artists generally having their own distinct style, technique and choice of underdrawing materials, analysis of these hidden layers can help to determine the legitimacy of a painting or provide insight into the methods of its production.
In order to use IR to successfully analyse underdrawings and other hidden details beneath the visible surface of an artwork, an Infrared light source is required to illuminate the artwork, with any light reflected back from various materials being captured and recorded using a specialist camera and filters.
Our VSC workstations and Crime-lite AUTO house these elements within a single unit, alongside specialist software, making the process of Infrared reflectography efficient, intuitive and, most importantly, effective. With this in mind, we will now consider case study examples of multispectral imaging and Infrared reflectography using these products:
VSC Case Studies
Northwestern University
Conservation and Multispectral Imaging with VSC 80
Jess Ortegon, graduate fellow at the Winterthur/University of Delaware Art Conservation Program, provides an excellent case study on forensic multispectral imaging in art and cultural heritage, (Looking a Little Deeper: Conservation and Multispectral Imaging), detailing research conducted at Northwestern University Library, which perfectly demonstrates the capabilities of the VSC 80 and the invaluable role it plays in specific conservation applications.
Working to conserve the university’s collection of manuscripts for further research, the multispectral imaging capabilities of the VSC 80 facilitate the non-invasive and non-destructive analysis of fragile manuscripts, allowing conservators to identify a range of materials present in the artefact, including adhesives, pigments, coatings and structural elements, with this information informing the optimal treatment methods, or whether to avoid any conservation action altogether if there is a significant risk of damaging or destroying the document.
NUL has over 5,000 Arabic script materials in their collection, dating from the 19th and 20th centuries. As a valuable resource for ongoing scholarly research, conservation of the collection is vital, with staff using multispectral imaging to conduct analysis of the papers and inks used and identify watermarks that would otherwise be invisible. The findings from this analysis are valuable in themselves to researchers studying the provenance of the materials, as well as informing treatment decisions by the conservators.
“We’re using the VSC80 for all of our analysis in this project as it’s able to replace multiple pieces of equipment used for each MSI technique (light tables, UV lamps, specialized IR cameras). It also has consistent, reproducible results, which is very important when recording and sharing results from such a large collection.”
PAPER ANALYSIS
Analysis of the manuscripts begins by using transmitted light to examine physical characteristics of the paper, in the hope of revealing information relating to its manufacturing processes, including laid and chain lines or watermarks. Through magnification, measurement and annotation of images of the manuscript, the VSC 80 provides examiners with detailed and accurate information on the density of laid and chain lines and the size of any watermarks present, with watermarks being used by researchers to gain insight into the geographical source of the paper stock and related trade and commerce routes.
INK ANALYSIS
Inks are analysed under both UV and IR illumination, with UV being used to observe fluorescence and IR indicating whether radiation was reflected or absorbed by the ink. While identifying inks with certainty is rare, gaining an understanding of their properties can help to identify similarities and differences amongst various inks, providing further valuable information for future research. The VSC stores the illumination parameters alongside each image, allowing examiners to easily compare the response of other inks under the same conditions.
REVEALING HIDDEN TEXT
Ortegon outlines the process by which multispectral illumination is used to reveal important hidden text on a letter without the risk of damage. The letter in question, from French-American artist and naturalist John James Audubon to his family, had previously been repaired by being adhered to another piece of paper which obscured important postage details, such as stamps, seals and the recipient’s address. To access this information, conservators considered removing the paper backing, however further investigation suggested the letter was written in water-soluble ink and such a procedure could cause significant damage.
To mitigate any risk to the document, conservators again turned to the multispectral imaging capabilities of the VSC 80, initially using transmitted light to observe the address and pinpoint its location on the reverse of the letter. IR illumination and filters were then employed to increase the legibility of the address, isolating it from other text by examining the reaction of different materials under precise radiation levels, a process which also revealed previously invisible stamps and fold lines. In this instance MSI proved invaluable, providing valuable information to researchers while avoiding potentially destructive or invasive treatment.
“Our observations and analysis using the VSC 80 will help to better contextualize the materiality of our collections and continue to mitigate potentially risky treatments”
View the article for images:
Looking a Little Deeper: Conservation and Multispectral Imaging
Ackland Art Museum
VSC 8000, Rembrandt Drawing
Ackland Art Museum curator, Dana Cowen, and paper conservator, Grace White, used the multispectral imaging capabilities of the VSC 8000 to examine a rare Rembrandt drawing from the Museum’s Peck Collection, revealing previously unknown and intriguing details which would otherwise be invisible to the naked eye.
During examination under IR illumination, they discovered anachronistic details in the drawing that had been added with a different material to the iron gall ink used by Rembrandt. The discovery was possible as iron gall ink transmits under Infrared light, becoming nearly invisible, whereas the more recent carbon ink present in the drawing absorbs Infrared, becoming darker and more visible. To the naked eye iron gall ink is dark enough to prevent the carbon ink from ever being discernible.
It is believed the carbon ink lines were added by a previous owner of the drawing to visually repair a degraded area of iron gall ink, in an attempt to improve the piece. This discovery provides researchers and students with an insight into the past lives of an object, and how it can best be preserved for future generations.
VSC at The Courtauld
Traces: Renaissance Drawings for Flemish Prints (18 Jun – 25 Sep 2022) at The Courtauld Gallery offered visitors the opportunity to look below the surface of the work of some of the most renowned Netherlandish artists of the Renaissance era.
Using the VSC 8000/HS, researchers were able to reveal traces left by the artists and craftspeople who produced many of the designs for the burgeoning Antwerp print trade throughout the 16th-century.
The video demonstrates how the process of multispectral imaging was used to analyse a drawing, by Jan van der Straet and engraved by Philips Galle, to gain valuable insight into the working methods of the draughtsman and engraver, revealing traces that would otherwise be near-invisible to the naked eye.
The Art of Experiment: Parmigianino at The Courtauld (5 Mar – 5 June 2022), a collaboration involving research students at The Courtauld, aimed to shed new light on the work of the pioneering Renaissance artist.
In preparation for the exhibition, technical examinations were conducted on the featured drawings, revealing two new drawings hidden beneath historic mounts. The initial discovery was made on the back of the Study for the Coronation of the Virgin for Santa Maria della Steccata, Parma, where Infrared reflectography revealed a male nude drawn on the reverse side.
In the video, Courtauld Conservator of Works on Paper, Kate Edmondson, uses a VSC 8000/HS to demonstrate a range of techniques that were used in preparation for the exhibition, exploring the drawings to reveal previously undetected details.
Crime-lite AUTO Case Studies
Cultural Heritage Agency of the Netherlands (RCE)
‘Lab on the Road’
In Autumn 2021 the Cultural Heritage Agency of the Netherlands (RCE) began their ‘Lab on the Road’ project, with researchers using mobile research equipment to conduct examinations and analysis of artworks and artefacts on-site at 8 museums across the Netherlands by the end of 2023. Such was the success of the project that the lab will be hitting the road again in April 2024.
Much of the success of the project can be attributed to advancements in portable forensic science technology and the devices made available to the researchers, with the foster+freeman Crime-lite AUTO being included in an arsenal of equipment alongside XRF scanners, microscopes and spectrometers. The portability and agility of the device, alongside its powerful multispectral illumination capabilities and integrated multispectral camera makes it an ideal choice for forensic multispectral imaging in art and cultural heritage applications, and foster+freeman were delighted to learn of its successful contributions to the project, resulting in some significant finds.
Crime-lite AUTO chosen to examine Mount Athos
Mount Athos, also known as the Holy Mountain, is an autonomous monastic state within Greece which holds great significance in the Eastern Orthodox Christian tradition. The site was designated as a UNESCO World Heritage Site in 1988, recognising the cultural significant of its historical monastic heritage and the unique ecosystems found on the mountain.
Consisting of 20 Eastern Orthodox monasteries and often referred to as the “Garden of the Virgin Mary”, Mount Athos is considered one of the most important spiritual centres in the Orthodox Christian world and attracts pilgrims from around the world.
A team of experienced conservators selected the Crime-lite AUTO when embarking on a trip to uncover hidden details within the Byzantine artwork of Mount Athos. Through the use of a combination of UV, visible, and Infrared imaging, the team of experts successfully revealed significant features in the artworks that had remained hidden from view for hundreds of years. The portability of the device proved vital to the success of the project, where moving the artworks to a lab setting would have been impossible.
Broader Applications: ffTA
While multispectral imaging and Infrared reflectography play a key role in the examination and analysis of artworks and artefacts, there are a plethora of other forensic methods which can be utilized in these applications, including microscopy, spectrometry and light polarisation, which can be conducted using the foster+freeman ffTA.
The ffTA is a powerful and flexible multi-functional system that provides a range of analytical facilities on a single microscope. By switching from module to module the operator is able to perform a wide range of analytical tasks and extract the maximum amount of forensic information in the shortest possible time.
MICROSCOPY
At the heart of the ffTA is the Leica DM2700M laboratory microscope, a device whose ancestors have been the primary tool of the art investigator or authenticator for centuries. This microscope is combined with high power LED illumination, creating a unique modular system which enables the examiner to add required functions and quickly switch between them using an optical multiplexer.
Microscopy is a key method in observing craquelure, tiny cracks which appear in a paintings surface over time, the analysis of which can help to identify the provenance and authenticity of an artwork. Acting much like a fingerprint, craquelure can be used as a unique identifier for a painting, with artworks from different climates, countries and time periods having different craquelure patterns. Microscopy also allows the investigator to get a detailed look at how paint has been layered on an artwork and if paint has been added anachronistically: a telltale sign of a fraudulent piece.
SPECTROSCOPY
The ffTA offers modules which allow the user to undertake multi-wavelength Raman Spectroscopy and UV-Vis-IR Micro Spectroscopy. These techniques can be used to identify the properties of particular materials found in an artwork or artefact, and compare them with other known quantities to determine the legitimacy of the subject piece.
LIGHT POLARISATION
Consisting of a pair of polarizers, a retardation plate, and a 360-degree circular rotating specimen stage with Vernier scales, this ffTA module enables birefringence to be measured to an accuracy of 0.1 degrees, and is highly effective in the detection and identification of fibres, making it an ideal tool for the examination and analysis of tapestries, historic clothing and other fabrics of cultural significance.
Conclusion
Having explored how our VSC workstations and Crime-lite AUTO are being used for forensic multispectral imaging in art and cultural heritage applications, it is apparent that each product possesses the capabilities to become invaluable tools for professionals working in specialisms across the field. We can also see that while these two products facilitate the same key technique of multispectral imaging, the respective methods by which they achieve this make them each ideal for specific applications, with the Crime-lite AUTO in particular representing a key technological development in the study of in-situ artworks and artefacts.
We also briefly touched on the ffTA, the potential cultural heritage applications of which are as-yet not fully explored. With the same holding true for other products in our range, such as the powerful DCS 5 system, we look forward to exploring the broader applications of our product range and the opportunities for discovery they hold.
We believe the development of technologies found in our VSC workstations and Crime-lite AUTO clearly represents a time of opportunity for researchers, examiners and conservators within the world of fine art and cultural heritage to advance the field and continue to explore, protect and learn from the artworks and artefacts of our cultural past.
As manufacturers, and researchers in our own right, it is exciting to be involved in sectors beyond law enforcement and border security, particularly when such valuable discoveries are being made. We look forward to continuing to develop best-in-class products which excel in fine art and cultural heritage applications, attending related future events and building meaningful working relationships in the sector.
Learn More
VSC® 8000/HS
Advanced Forensic Analysis of Manuscripts, Paintings, Documents, Canvases and more…
VSC® 900
The Complete Solution for the Analysis of Artworks and Cultural Artefacts
Crime-lite® AUTO
A Compact and Portable Solution for the Multispectral Examination of artworks
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