History of artistic diagnostics and technical analysis
Specifying in chronological terms the recognition of the methods of scientific analysis in the examination of works of art is not easy as it is evident that for many centuries there were only “isolated attempts at first empirical, then ‘scientific’, based on chemical analysis and applied to materials and objects mainly of archaeological interest” .
As a demonstration of what we can define “first empiricism” applied to the study of the work of art, the example mentioned in 1732 by Tassi is relevant . In fact, it is said that the Bergamo painter Vittore Ghislandi, also known as Fra ‘Galgario, possessing a Tiziano painting had made “attempts” that Paolo Bensi does not hesitate to define as “stratigraphic tests” since with “a small knife he had investigated the structure of the pictorial layers” .
In the Eighteenth Century, attention began to focus on the merits of the analyzes that involved the use of optical instruments and from 1780 the physicist Jacques Alexandre Cèsar Charles, also known as a precursor of the Gay Lussac principle on the thermal expansion of gases, applied these theories on the panels preserved in the Louvre museum .
The first publications on the analysis and identification of pictorial material and support date back to the early Nineteenth Century, the first is a document written in France by Jean Antoine Chaptal  which is followed shortly after by one from the eminent scientist English Sir Humphrey Davy , both studies dealt with pigments and aggregates on encaustic murals found in Pompeii.
The basis of a collaboration between scientists and art historians
But it is only from the second half of the Nineteenth Century that the foundations of a collaboration between scientists and art historians begin to be laid  and that methods and means of a physical nature are added to chemical analyzes; the dedication to a better understanding of the secrets of the ancient masters’ painting techniques begins by identifying all those alteration processes to ensure a better conservation of the works.
In the second half of the Nineteenth Century, the collaboration between science and art became a fait accompli. From the first scientific works that have found hospitality in some periodicals, we have moved on to a whole literature specialized in increasingly important and numerous publications. 
In the early Twentieth Century, the Englishman Arthur Pillans Laurie, whose chemical studies on artistic materials span half a century, published a series of articles and books on the research carried out by him. The volume, Pigments and Mediums of the Old Masters , published in 1914 is to be considered his greatest contribution to analytical studies. It must be emphasized here that in this period the chemical analysis necessarily had to evolve and improve in an analysis applied to ever smaller quantities of samples taken from the work in question.In 1930, many short studies on the microchemical identification of pigments were published: the excellent monograph by the Dutch A. Martin de Wild, The Scientific Examination of Paintings , published in 1929, was for a long time considered the most relevant study on the Flemish Masters’ technique. Other fundamental contributions are due to the German scientist Alexander Eibner who published numerous articles on microchemistry in the examination of painting in “Mouseion” and “Angewandte Chemie“. We also owe to him the pioneering work on the use of the ultraviolet lamp in the study of fluorescence in antique paintings . The use of ultraviolet light sources in the investigation of works of art began at the end of the 1920s with the creation, by the American physicist Robert William Wood, of a glass filter based on nickel oxide capable of blocking visible radiation and remain transparent to ultraviolet radiation. With this particular glass filter, sources only emanate ultraviolet radiation (also called “Wood lamps” or “black light sources”) which induce fluorescence phenomena on many substances used in painting .
It is important to note that after the work of Eibner and other researchers, which were published around 1930 , there have been no publications on the subject for many years regarding this important area of investigation. The Central Research Laboratory for Objects of Art and Science in Amsterdam with Rene De La Rie will carry out the studies on the fluorescence spectrum of pictorial materials and painted surfaces, the results of which were published in 1982 .
Identification of materials
Previously a student of Eibner, H. Hetterich, in “Microchemie“ , wrote important essays on microchemical methods for the identification of pigments and mediums in painting. On the same subject and in those same years both Selim Augusti and Rutherford J. Gettens  published other fundamental essays.
The project for a manual on the identification of materials in painting should also be remembered, in 1958 Gettens created it with the collaboration of Joyce Plesters of the National Gallery in London and the sponsorship of the International Institute for the Conservation of Historic and Artistic Works. The manual was supposed to serve as a reference tool for chemists, conservators, restorers and collectors. The vastness of the project required the cooperation of several laboratories, initially the study covered the analysis of about seventy pigments and fillers, the most commonly present in both ancient and modern paintings. Data collected for each pigment included: chemical composition, history of the early period of use and discovery, geographic distribution and frequency of use in antiquity, methods of preparation, optical properties, chemical properties, microchemical tests, X-ray diffraction, curves of spectrophotometry.
Studies on the analysis of pictorial materials were interrupted during the Second World War, and resumed only in the 1950s with the research of Paul Coremans  and his colleagues, of the Royal Institute of Artistic Heritage of Belgium, related to Van Eyck and other Flemish painters.
In 1956 Joyce Plesters published his well-known article, in “Studies in Conservation” , rich in documents and illustrative tables for the recognition and identification of the pigments taken from the pictorial surface. His merit was also to underline how a painting represents not a surface to be investigated but a stratigraphic structure, thus stimulating new methods of investigation, such as X-rays and infrared photography.
The application of X-rays to the examination of paintings
In the field of physical investigation, photography, as an ideal means of documentation, is accompanied by the contributions made by the information obtainable through the application of X-ray radiography on pictorial works. No one would ever have suspected that when Wilhelm Konrad Rontgen was awarded the Nobel Prize in 1901, his discovery would become an “essential tool of artistic investigation” . Like many others discoveries, X-rays were discovered by “chance”. The physicist Rontgen, in 1895 during some experiments carried out with cathode-ray tubes, observed that from the anode of such tubes radiations of a mysterious nature were emitted and that they were capable of passing through solid bodies and impressing the photographic plates placed behind them. These radiations, with the name of X-rays, were used in the medical field to “photograph” the inside of the human body. The importance of its use in the artistic field was recognized by the discoverer of X-rays himself, who, in 1896, was able to see a painting from the school of Raffaello under an Eighteenth-Century landscape .
That same year, in an editorial article of “Electrical Review”, the following was stated: “It is very likely that this application (the application of X-rays to the examination of the paintings) will prove invaluable to art dealers allowing them to discover frauds” .
“It was not a wrong prediction: to the merchant or in general to those who had an interest in ascertaining that the quality of a pictorial work or its authorship were not lying, the laboratory tests, and above all the radiography, were of great use, and could have been even more useful if they had been correctly understood”. The examination to which a painting was subjected on the occasion of a transaction or in other similar circumstances was unfortunately, as recent studies highlight, entirely “occasional in order for it to be considered serious. This does not only reffer to the economic interest of the merchant or of his client.The curiosity interest of third parties was much more harmful. Unfortunately, there have sometimes been some lucky cases – the case of the examination limited to a single painting which reveals its counterfeiting or that of the examination which, on the contrary, reveals a Mantegna or at least a Crivelli under an unfortunate repainting – which entered immediately in the supply of savory anecdotes with which, from time to time, a journalist could easily embellish a popular article, most of the times in a rotogravure newspaper “. As scholars have repeatedly stressed, the possibility of drawing fruit from an isolated examination has distracted, for long time, attention from the opportunity to carry out a systematic analysis instead , an analysis that is applied to large groups of works by a specific author capable of providing a true comparative and decisive judgment for the attribution and verification of the authenticity of the paintings. If it is true, however, that the greatest number of publications on the subject dealt with radiography solely as a function of restoration and therefore of conservation, providing us with the evidence of individual paintings, it is equally true that already, in the second and third decade of the Twentieth Century, there were also publications specifically aimed at underlining the importance that radiographic analysis had for an artistic evaluation of the work.
It became more and more evident that each artist had a personal brush stroke and these brush strokes, visible on the X-ray, were as characteristic as fingerprints in order to be able to make a judgment based on their character. The need for the use of radiographic examination for the study of a single artist had been foretold, before the 1920s, by the German physicist Karl Kùnig who had concentrated his work on the comparison of radiographies of Albrecht Durer’s paintings . The analysis of X-ray absorption by the different pigments involved an ever-increasing number of scholars; thanks to new contributions made by European scientists such as Töpler, Heilbronn and Chéron the first methodologies were established .
The importance of founding an X-ray archive
The project for the foundation of a real radiographic archive was laid out by E. W. Forbes, curator of the Fogg Museum of Harvard University in Cambridge, Massachussets, who, between 1920 and 1925, envisaged the collection of radiographic plates of all the masterpieces collected in museums of the old and new continent. This important research program will be carried out by Alan Burroughs who proposes to implement the radiographic collection not only for conservation purposes, but as a valid supplementary tool for art history scholars. He published a remarkable article in 1938  but the radiographic documentation on which his studies are based on remains too limited to be considered exhaustive and to promote or solicit new research.
In Italy it was Mariani  and Mancia who defended the use of radiography for a systematic, and not only conservative, study of artistic works, the latter also stressed the importance of the foundation of a national radiographic archive .
The merit of having, for the first time, carried out a historical-artistic study also based on an extensive radiographic documentation belongs to Antonio Morassi, his 1942 annotations on Giorgione’s work were and remain extremely important, there he stresses that “the the basis of every art critique must be a complete knowledge of the physiology of the work that has to be studied(…) the Rontgen rays have offered, from a few years ago, a notable contribution to the branch of Art History” .
Also worth mentioning are Bazin’s studies on Corot  , Rees’ Jones on Poussin  and Wolters’ monograph  , as well as those of Hours Miedan on Poussin, Rembrandt and Leonardo, presented, the latter, to complete the exhibition “Hommage à Léonard de Vinci” .
In Italy, starting from the 1970s, the brilliant studies of the radiologist Ludovico Mucchi on Pietro Longhi  , on the Leonardeschi (1972)  , on Tiziano  (1977, in collaboration with Precerutti Garberi) and on Giorgione  (1978, in collaboration with Terisio Pignatti) must be remembered. His analysis on the vast sampling of the Venetian landscape painters of the ‘700 remains exemplary: 216 paintings meticulously studied and compared in their radiographic characteristics “so as to breach into the most intimate secret of the creation of images” .
The infrared reflectography has been used in the study of art objects since the mid-1960s, mainly by students engaged in research into Flemish primitive painting. Subsequently, this investigation tool spread, becoming part of the technical equipment of restorers, conservators and art historians .
In the early postwar years, in some American universities, a current aimed at depriving physics laboratories of the exclusivity of this type of research was born.
Since the 1960s, the need to place an analysis laboratory alongside museums and other restoration institutes becomes more noticeable. As stated by the two chemists Matteini and Moles, in “this perspective of rationalization and greater awareness of the interventions (…) the scientific research activity for paintings on canvas and wood favors the cognitive aspects of works rather than conservative ones” .
The search for spectacular effects
It is important to note how, starting from the Seventies, artistic diagnostics had a sort of acceleration for which there was no longer an exhibition or a catalog without scientific documentation. However, it is important to observe how art historians, conservators and restorers could be perplexed when faced with the presentation of the applications and results of scientific documentation techniques. The search for spectacular effects to offer during the various events highlighted the lack of methodology and true collaboration between those who performed the exams and those who had to materially intervene on the work or study it . Fortunately, the seriousness of the research has been able to correct the phenomenon of its trivializing theatricalization as demonstrated by the most recent publications where, in fact, the historical-artistic discourse and the more purely scientific one articulate and integrate with each other. Therefore, as a demonstration of this, see the brilliant monographic studies on the work of Bellini, Titian, Caravaggio, Pietro da Cortona and the four major Venetian landscape painters to whom we refer in the bibliography.
Manfredi Faldi, La documentazione materiale come supporto e verifica dell’analisi storico-stilistica nelle opere pittoriche, Florence 2003
S. Augusti, Les mèthodes d’analyse appliquees aux oeuvres d’art et aux antiquietes, in “Recent advances in conservation“, London Buttherworths, Ed. Thomson 1963, p.20.
Cfr. F. M. Tassi, Vite de’ Pittori, Scultori e Architetti Bergamaschi, Bergamo I793, edizione critica a cura di F. Mazzini, Milano 1979 e lo studio monografico di M. C. Gozzoli, Vittore Ghislandi detto Fra’ Galgario, estratto da I pittori bergamaschi, Il Settecento, I, Bergamo, Bolis 1981.
P. Bensi, La vita del colore, Genova, Neos Edizioni 2000, p. 77.
Cfr.a proposito M. Hours Miedan, Analyse scientifique et Conservation des Peintures, Office du Livre, Fribourg 1976, poi nel Catalogo della Mostra che sul tema si è tenuta a Parigi, AA.VV., La Vie mystérieuse des chefs-d’ouvre-La science au service de l’art, Paris, Editions de la Réunion des Musées nationaux 1980. Della stessa autrice si veda anche, A la découverte de la peinture par les méthodes physiques, Arts et métiers graphiques, Flammarion, Paris 1957 e Les secrets des chefs-d’oevre, Paris, Ed. R. Laffont 1964.
Cfr. J. A. Chaptal, Sur quelques trouvées a Pompeia, in “Ann. Chim.”, 10, 1809, pp. 21-31
Cfr. H. Davy, Some experiments on the colours used in painting by the ancients, in “Transaction of the American Philosophical Society”, 105, 1815, pp. 97-124
Cfr. P. Bensi, Scienziati e restauratori nell’Italia dell’Ottocento, una difficile convivenza, , in Giovanni Secco Suardo. La cultura del restauro tra tutela e conservazione delle opere d’arte, atti del convegno internazionale di studi, Bergamo 9-11 marzo 1995, “Bollettino d’Arte” supplemento al n. 98, 1996, pp. 25-32
 Cfr. S. Augusti, cit., 1963, p.20.
A. P. Laurie, The pigments and mediums of the Old Masters, London 1914, e dello stesso autore si citano qui, Un laboratoire pour l’examen des peintures. Appareils pour les rayons X, “Mouseion“, Paris, vol. 17-18, 1932 e The Tecnique of Great Painters, London 1949
A. Martin de Wild, The scientific Examination of Paintings, London 1929.
A. Eibner, L’examen microchimique de tableaux et décorations murales, in “Mouseion“,13-14,1931, pp. 70-92; si veda anche, dello stesso autore, L’examen microchimique des agglutinant,s ivi, 20, 1932, pp. 5-22 e cfr. anche, Zum gegenwartigen Stand des naturwissenschaftlichen Bilderuntersuchung, in “Angewandte Chemie“, 45, 1932, pp. 301-307 e L’Analyse Microchimique des Colours, in “Mouseion“, 29-30, 1935, pp. 113-126.
Cfr. a proposito lo studio di A. Aldrovandi e M. Picollo, Metodi di documentazione e indagine non invasive sui dipinti, Padova, ed. Il prato 1999
Cfr.il saggio di A. Eibner, Les rayons ultraviolets appliqués à l’examen des couleurs et des agglutinants, in “Mouseion“, 21-22, 1933, pp. 32-68. Si ricordano qui anche gli studi di H.Wolff e W. Toeldte, Zur Fluoreszenz– Analyse der Ollacke, in “Farbenzeitung“, 31, 1926, pp. 80-81 e, degli stessi autori, Ein Beitrag zur Kenntnis und Prufung der Harze, in “Farbenzeitung“, 31, 1926, pp. 2503-2505 e l’articolo, Leinol im Ultraviolettlicht der Analysenquarzlampe, in “Farbe und Lack“, 31, 1926, pp. 509-510
R. De La Rie, Fluorescence of paint and varnish layers, in “Studies in Conservation“, 27, 1982, pp. 1-7, pp. 65-69 e pp. 102-108.
Cfr. a proposito i seguenti articoli di H. Hetterich, Uber die Anwendung mikrochemischen Methodem bei pigmentuntersuchung von Gemalden, in “Mikrochemie“, Emich Festschrift, 1930, pp. 152-181; e Uber Mikrochemische Bilduntersuchung, in “Mikrochemie“, X, 1931, pp. 15-41
Cfr. S. Augusti, cit., 1963 e, della stessa autrice, si ricordano i seguenti studi, Metodo sistematico per il riconoscimento microchimico dei colori minerali, in “Mikrochemie“, 17, 1935, pp. 1-10 e pp. 344-355 e I colori pompeiani, Roma, De Luca 1965.
Cfr. R. J. Gettens e G. L. Stout, The stage microscope in the routine examination of paintings, in “Technical Studies in the Field of Fine Arts“, 4, 1936, pp. 207-233; e degli stessi autori si veda anche, Painting materials: a short encyclopedia, New York, Dover Publications 1966. si veda inoltre l’intervento di R. J. Gettens e E. M. Mrose, Calcium sulphate minerals in the ground of Italian paintings, in “Studies in Conservation“, 1, 4, 1954, pp. 174-189.
Cfr., P. Coremans, Technishe inleiding tot de stude van de Vlaamse Primirieven, in “Gentse Bijdragen tot de Kunstgeschiedenis“, XII, 1950, pp. 116-117 e, ancora P. Coremans, R.J. Gettens e Thissen, La Technique des Primitifs flamans in “Studies in Conservation“,I, 1952, pp. 1-29.
J. Plesters, Cross-Sections and Chemical Analysis of Paint Samples, in “Studies in Conservation“, 11, 1956, pp. 110-157.
Cfr T. Pignatti, Prefazione al volume di L. Mucchi e A. Bertuzzi, Nella profondità dei dipinti, Milano, Electa 1983, p. 9.
Cfr. L. Mucchi e U. Tolomei, Alla ricerca di Pietro Longhi, Milano, Achille Mauri Ed. 1970, p.10.
 Cfr. A. M. Dewild, Testing Pictures by the Roentgen Rays, in “Electrical Review“, 40 (607), 1014, London 1897
Queste ultime citazioni sono tratte dallo studio di L. Mucchi e U. Tolomei, cit., 1970, p. 10
Cfr. L. Mucchi e U. Tolomei, cit. 1970
Cfr. A. Chéron, La radiographie des tableaux, “Académie des Sciences”, 13-12-1920, n. 172, pp. 57-59; Expertise radiographique des tableaux, Communication faite à la Société Francaise de Photographie, séance générale du 25 févr. 1921; Etude des tableaux par la radiographie, Communication faite à la Société de radiologie Médicale, Parigi 1921
A. Burroughs, Art Criticism from a Laboratory, Boston, Little Brown and Co. 1938.
Cfr. V. Mariani, I raggi X e la critica d’arte, in “Emporio”, 85, 508, 1937, pp. 187-196
R. Mancia, L’esame scientifico delle opere d’arte ed il loro restauro, 3 Vol., Milano, Hoepli 1944-45.
A. Morassi, Esame radiografico della “Tempesta” di Giorgione, in “Le arti”, a. 1, fasc. VI, agosto-settembre 1939, pp. 567-570 e poi nella monografia, Giorgione, Milano, Hoepli 1942.
G. Bazin, Peintures de Corot, vraies ou fausses, in “Bulletin du laboratoire du Musée du Louvre”, giugno 1956, Parigi 1956, pp. 304-308.
S. R. Jones, Notes on radiographs of five painting by Poussin, in “Burlington Magazine”, 1960, pp. 304-308.
Cfr. C. Wolters, Die Bedeutung der Gemaldechlurchleuchtung mit Rontgenstrahblen fur Kunstgeschichte, M. Prestal Verlag, Frankfurt 1938 e lo studio Anmerkungen zu einigen Rontgenaufnahmen nach Gemalden des stadelschen Kunstinstitut, in “Stadel Jb”, 7-8, Frankfurt, 1932, pp. 228-240.
M. Hours Miedan, La radiographie des tableaux de Léonard de Vinci, “Revue des Arts”, 4, Paris, Ed. des Museés nationaux 1952, si veda anche dello stesso autore lo studio, A la découverte de la peinture par les méthodes physiques, cit. 1957
L. Mucchi – U. Tolomei, cit., 1970
L.Mucchi e M. Precerutti Garberi, I leonardeschi ai raggi X, Milano 1972.
L. Mucchi e M.Precerutti Garberi, Omaggio a Tiziano, Milano 1977.
L. Mucchi, Caratteri radiografici della pittura di Giorgione, Firenze, Alinari 1978
Si cita da T. Pignatti, Prefazione al vol. di L. Mucchi e A. Bertuzzi, cit., 1983, p. 10.
Cfr. William. A. Real, Infrared reflectografy at the Cleveland Museum of Art: Paintings, Objects, Manuscripts, “AIC”, 1985.
Cfr., AA.VV., M. Matteini e A. Moles, Il laboratorio scientifico nella ricerca e nella pratica operativa del restauro dei dipinti, in Problemi di restauro. Riflessioni e ricerche, Firenze, Edifir 1992, pp. 213-222
Cfr. M. Faldi e C. Paolini, Tecniche fotografiche per la documentazione delle opere d’arte, Quaderni dell’Istituto per l’Arte e Restauro, n.1, Firenze 1987.