Physical Sciences ︱ Professor Costas Balas

approach is to combine spectroscopic methods with imaging methods. Stripping paintings Spectroscopic methods are ideal for accurately determining which chemical elements are present in a particular region but imaging methods have of their secrets with very high spatial resolution and can therefore disentangle differences in even small, detailed areas of the painting. This combination is known hyperspectral imaging as hyperspectral imaging and Professor Costas Balas at the Technical University of Crete, Greece and his research What lies beneath hundreds rt restoration is a difficult The answer lies in tools typically used group are experts in improving of years of paint? Professor business. A single painting in analytical chemistry. Most of these and developing hyperspectral imaging Costas Balas at the Technical A will use numerous pigments involve shining non-visible wavelengths technologies for both medical University of Crete, Greece to create a wealth of different colours of light through the painting, including and art conservation applications. is privy to some of the secrets but while those colours might be X-rays and infra-red radiation, as these of the great Renaissance indistinguishable by eye, each of those are not completely absorbed by the HYPERSPECTRAL DEVICES masters with his hyperspectral pigments may in fact have a different surface paint layers, unlike visible light. Professor Balas’s interest in imaging devices. Such devices chemical composition. Even worse, Unfortunately, such spectroscopic hyperspectral imaging was originally can be used to identify not just different pigments or regions of the techniques are very expensive and motivated by his work in the field Hyperspectral analysis of the palimpsest (72 verso) (Mount Athos Monasteries-Greece). Regular colour what chemicals are present painting may have been treated with provide point-by-point information. of cancer diagnosis and biomedicine. photography (top) shows only the newer script entitled “Mandona Anthems” which has been dated as in pigments on the surface layers 13th century AD. There is an older invisible script, however, dated between the 10-11th century AD, entitled different binding materials and varnishes, This means that each section of the Here, there is a need for devices that “Porphyrogennetus”, which is revealed with hyperspectral imaging. The fusion of selected spectral of paintings, but also what lies which will also affect the types of solvents painting must be meticulously scanned can successfully and accurately profile images made the visualisation of both the new (vertical script) and the old (horizontal script) possible. underneath. and materials that can be used for with the incoming X-rays or infra-red and image tumours within the body cleaning or touching up certain areas. to record all the chemical information as part of the diagnostic process on different sections of the painting. but there are a number of features The team found a number of surprising If colour alone is not a reliable indicator It may also be necessary to tune of the technique that have meant of the pigments and chemicals used the wavelengths of the incident light it can be applied to a diverse range results that only hyperspectral imaging in a painting, how can art experts to see different elements. of applications, including art restoration could have unearthed. and scientists identify what materials and identification. have been used with a great degree of Given how time-consuming point- the infra-red. Using these wavelengths with ultraviolet and infra-red detection accuracy, all in a non-destructive manner? by-point scanning is, one alternative A hyperspectral imaging device of light in the infra-red allows Professor that provide more definitive chemical works by simultaneously recording Balas to peel back the layers of paint assignments and are sensitive not just spectral and spatial images to make to what lies on the canvas underneath. to the surface layers. three-dimensional data sets. A spatial The flexibility of the wavelengths that image is like a photograph that shows can be used with hyperspectral imaging SEEING THE CANVAS the location of all the different objects has many advantages for dealing with Professor Balas and his team have been in the frame. However, as the spectral complex materials such as paintings. able to use this technology to study information can only be obtained for The use of visible light is important one of Doménikos Theotokópoulos’s, a limited number of wavelengths per for identifying colours and pigments, otherwise known as El Greco, spatial image, this means only certain coloured objects are recorded in a single image, so it would be like taking a photograph which would only show green objects. To make up a full three- dimensional image, another photograph would be taken, that would only show blue objects, then red objects and so forth until all the wavelengths of interest had been covered and the full Fluorescence imaging combining spectral scene could be created. images of El Greco’s St Francis of Assisi reveals invisible conservation interventions. Materials used for conservation are similar to the In practice, as the human body and background color but their different chemical paint absorb visible light, the imaging composition is evidenced by the different The hyperspectral camera, developed by Professor Balas and his team, (left) captures a series of fluorescence emission pattern. ranges of the hyperspectral imaging monochromatic images across the spectrum, building up the so-called spectral cube (right). This data devices span from the ultraviolet to structure assigns a full spectrum to every point in a scene, giving information on its chemical composition.

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Malachite Verdigris Research Objectives References Balas, C., Epitropou G., Tsapras A. and Hadjinicolaou N., Green Earth Professor Balas uses and develops hyperspectral imaging (1125) (2018) Hyperspectral imaging and spectral classification for Green Earth technology in art conservation and in biomedical diagnosis. (4081) pigment identification and mapping in paintings by El Greco Green Earth and his workshop, Multimedia Tools and Applications, 77, (4082) Detail 9737–9751. Hyperspectral analysis of “El Espolio” by Jorge Manuel (El Greco’s son). Spectral mapping of a detail, shown in the red frame, combined with machine learning methods allows for the identification of malachite pigment non destructively. Areas with malachite are artificially colored with red for the purpose of facilitating Costas Balas PhD the visualisation of the pigment’s distribution in the painting Professor | Director Electronics Lab | School of Electrical & Computer Engineering Personal Response masterpieces, ‘The Baptism of Christ’. Technical University of Crete Thought to have been painted in Professor Balas’s interest in hyperspectral University Campus Acroterion 73100, the early 1600s, the painting depicts imaging was originally motivated by his Chania, Crete What are the unique challenges of imaging art pieces? a complex scene involving both the Greece Art pieces are very complex in nature with multiple heavens and the earth, where Christ work in the field of cancer diagnosis. layers and chemicals contributing to image formation. stands with St John the Baptist at Bio When referring to historic art pieces, construction his right. Strikingly, a number of figures extracted from the hyperspectral imaging colours and the techniques used to paint Costas Balas is a full Professor at the Electrical and materials are often unknown and therefore it is very difficult to develop material replicas to be used as are robed in bright greens, reds and indicated this ‘I’ was not a numeral as them often provide art historians with Computer Engineering department of the Technical reference for the analysis. yellows, giving a small indication part of the date, but actually intended many visual clues as to a painting’s age, University of Crete. He is a recognised expert and innovator of the complexity of the chemistry to be part of a nearby scene. which can in turn be verified by a more in- in biophotonics and hyperspectral imaging. He has Innovative platforms integrating hyperspectral imaging occurring on the campus. depth chemical analysis of exactly which patented and published life-saving, FDA-approved and machine learning methods emerge as a powerful While hyperspectral imaging may compounds were used where. photonic methods and imaging technologies for tool for addressing these challenging diagnostic/ The goal of the project coordinated be more efficient than point-by-point non-destructive analysis and for noninvasive diagnosis. He analytical tasks. by the Benaki Museum was to provide spectroscopic methods, the size of Hyperspectral imaging can be used teaches both graduate and undergraduate courses. technical information to art historians the painting posed some problems not just for identification and dating to allow them to date and authenticate for Professor Balas and his team. They but also for historical preservation. Collaborators the painting and to determine what were able to identify over ten different In cases where restoration is not possible The guidance and the data interpretation offered by the physical condition of the painting pigments used by El Greco and his due to the fragile nature of the object, the eminent Art Historian Professor Emeritus Nicos was to aid with conservation work. contemporaries on the painting, including imaging can be used to create digitised Hadjinicolaou and the experimental work conducted by my During this process, the team found lapis lazuli and azurite, but needed a records of particularly frail manuscripts. graduate students are gratefully acknowledged. a number of surprising results that only more efficient way of identifying them One example is the Codex Sinaiticus, hyperspectral imaging could have over the full scale of the canvas. To the earliest manuscript containing unearthed, including the numerals do this, they turned to machine learning the complete New Testament which ‘MDLXVI’, indicating the year 1566. This methods that, once they had been dates from the mid-fourth-century. date had gone previously unnoticed as trained to identify the spectroscopic Technical it had been overpainted, but the quality signatures of the various pigments, could The Codex Sinaiticus is currently kept of the spatial resolution from the imaging then automatically assign which pigments in four different locations, so as well University made it possible to unambiguously had been used to paint specific regions, as historical preservation, the goal resolve most of the date. speeding up the process immensely. of imaging the whole text also served the purpose of allowing a reunification of Crete There was one small complication to CAPTURING THE PAST of the complete text. The reunification this, though. Next to MDLXVI appeared While not all paintings have dates of the text through imaging gave some to be another I, which would indicate conveniently hidden under layers of ideas as to how the book may have the year to be 1567. Most other analysis paint, hyperspectral imaging can be used originally been bound and researchers techniques would have suggested to date paintings through a different now have a wealth of information on the additional ‘I’-like feature was approach. When chemists and artists the composition of the different coloured intended to be part of the date, owing alike found ways to create new pigments, inks used in the text, all of which have to its location and similarities in colour. this was often intimately related to the been made possible by developments However, the chemical information also development of new artistic styles. Their in hyperspectral imaging.

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