July 2020 · 1 FOCUS | Art and Science of NDT
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Vol. 19,13, No. 31 FOCUS The Art and Science of NDT at the Hermitage Museum by Alexander Iosifovich Kosolapov TNT WRITE FOR ! EDITOR’S NOTE Are you interested in writing for The This article is an excerpt from a research paper originally published in Russian in the journal NDT Technician (TNT)? Content for NDT World. It was translated into English courtesy of the editors of NDT World and TNT is focused for NDT practitioners was condensed for publication in The NDT Technician. We hope you enjoy this behind-the-scenes engaged in field applications of NDT. peek into nondestructive testing at the world-famous Hermitage Museum. Typical themes include interpretation skills, methodology, problem-solving procedures for everyday challenges, practical application of NDT with data the Scientific and Technical Expertise and results, and technology trends. Introduction Department (STED). Currently, STED Contributors to TNT earn three ASNT The history of the scientific and technical includes two laboratories: a technical and renewal points per published paper expertise at the State Hermitage Museum (min. 1000 words). If you have a in St. Petersburg, Russia, begins in the technology expertise laboratory and a topic you’d like to see published early twentieth century, the time when physics-chemical examination laboratory. in TNT, contact the editor: some chemists initiated their participation The staff includes 16 employees, mostly Jill Ross, Periodicals Editor in the development of procedures for the physicists and chemists, as well as a 1-614-384-2484; restoration of artworks and in solving biologist (botanist) and an art historian. email [email protected] other problems of a chemical nature. In STED’s main functions are as follows: l 1936, T.N. Sil’chenko created one of the to authenticate artworks l first X-ray rooms in a museum in Russia, to participate in restoration projects, which was later transformed into a physics in terms of the scientific development X-ray laboratory. In 1955, I.L. Nogid of procedures and creation of technical created a small chemical laboratory. These documentation l two laboratories existed independently to support operations on the of each other, at first as part of the classification of our collections restoration department, and then as part Described in this article are the main of the museum science department. In nondestructive testing (NDT) devices used The American Society for 1997, the laboratories merged to form in STED and some examples of their usage. Nondestructive Testing asnt.org ASNT...CREATING A SAFER WORLD! ® TNT · July 2020 · 1 FOCUS | Art and Science of NDT Unmasking Counterfeits One of the main functions of STED is to identify forgeries. The extent of business on the sale and purchase of artworks in the world amounts annually to many tens of billions of dollars, with the market prices for artwork continuously growing from year to year. It is natural that among the sold and purchased articles there will be falsifications or simply improperly defined articles. The history of forgeries goes far back, starting from the ancient times. The museum’s purchasing committee often comes across forgeries and imitations. Quite often it gives rise to disagreements when defining the authenticity of an object “by sight,” using history and stylistic similarities (methods traditionally used by professional art historians), together with an assessment on the basis of analytical methods (obtained by STED). (a) In general, scientific and technical expertise methods can be divided into two large groups: destructive methods (laboratory methods) that require taking a sample from the material, and nondestructive methods that do not require taking out a sample. In our view, however, this is quite a conditional division since there are methods that can be used in both versions. For example, Raman spectroscopy is a technique in which the object can be investigated using a Raman microscope both with taking a sample and without taking a sample, depending on the size of the investigated object. Also, many Raman sets are provided with remote probes suited for NDT of the nonvarnished surface of old paintings (old varnish provides strong luminescence, which masks the useful signal). Similarly, X-ray structural analysis can be used both for the whole object (nondestructive method) and for a sample taken from the material (destructive (b) method). Figure 1. Ian Provost’s “A Virgin with a Baby”: (a) original photo; (b) a preparatory drawing revealed by infrared reflectogram. 2 · Vol. 19, No. 3 Included in the group of traditional Thermal/Infrared Testing and proof of the fact that it is not a copy. This NDT techniques can be versions of optical Fluorescent Photography method also frequently reveals unreadable, microscopy, which allow an object placed “faded away” signatures of the artists. Infrared reflectography enables experts to on a table or easel to be tested directly. Another type of NDT examination used detect free carbon that can be contained These techniques represent radiographic is fluorescent photography. In this case, in paint-covered materials (for example, analysis in various wavelengths, from the paint layers of the painting produce a preparatory carbon or pencil drawing very soft rays for fluoroscopic viewing of luminescence. The absorbed radiation under the layers of paint). For this task a monetary notes or paper to very hard rays is in the ultraviolet (UV) region of the high-resolution camera is used. Camera for penetrating through heavier materials. spectrum, and thus invisible to the human resolution is 4K × 4K pixels and the In X-ray imaging there are a number of eye, while the emitted light is in the camera is equipped with an interference modern nondestructive techniques used, visible region, which gives the fluorescent filter mounted directly on the detector to namely X-ray emission imaging used for substance a distinct color that can be seen enable operation in ~1.7 µm wavelength. paintings that are opaque to X-rays. Finally, only when exposed to UV light. In Figure Figure 1a shows a photo of the painting there are many versions of computed 2, the “Lady’s Portrait” by K. Makovsky “A Virgin with a Baby” by the Dutch tomographic (CT) techniques. shows clear contrast spots on the lady’s artist Ian Provost (1465–1529) from Also included in this group are face and in the background in the form the Hermitage collection. An infrared specialized photography methods, including of visible luminescence. In this case, the reflectogram reveals a preparatory drawing fluorescent and infrared photography. X-ray spots are produced due to application of on this painting, as shown in Figure 1b. structural analysis and Raman spectroscopy zinc-titanium white alongside the lead The drawing does not coincide in all details can be used for the nondestructive white paint (which does not produce color with the final visible artwork of the artist investigation of minerals and gems. The luminescence), producing a brown-green (for example, compare the position of the same can be said about X-ray fluorescence color luminescence. Photographing the Virgin’s belt). The differences stand for solid analysis performed in the open air. Electron visible luminescence image caused by UV microscopy investigation is carried out, as a rule, on samples taken from materials, but in some cases, it can be considered an NDT method, provided the microscope chamber can accommodate the whole object under test. Destructive methods include X-ray structural and Raman analysis performed on samples, most versions of electron microscopy investigation, all types of chromatography analysis required for determining organic materials on paintings, infrared spectroscopy (in most cases), and practically all known methods for determining the age of materials, including thermo luminescence for ceramics and radiocarbon dating for organic materials. When testing, it is always desirable to have a reference artwork by the same artist made within the given period of time to compare with the article under investigation. Let’s now refer to the scientific and technical methods used in the Hermitage STED. Figure 2. K. Makovsky’s “Lady’s Portrait” showing visible luminescence generated by UV radiation. TNT · July 2020 · 3 FOCUS | Art and Science of NDT radiation is not only a useful nondestructive analysis (XFA). Nowadays, XFA is a pigments and other materials, and in many way to determine inscriptions on paintings standard analytical procedure widely used cases successfully competes with older X-ray but also a good means to restore discolored in museums. The technique is fast and structural analysis methods based on the (faded away) texts written with iron gall effective, and can reveal paint on a painting recording of diffraction of monochromatic ink on documents. that does not coincide with the assumed X-ray radiation on the crystal lattice of time of creation, as well as determining minerals and metals. To investigate X-ray posterior types of metal alloys in articles diffraction of materials (when determining Radiographic Testing and evaluating composition of enamels, crystal structure), two devices are used in A good example of X-ray radiography glasses, and more. the Hermitage. One is a diffractometer in our workshop was of Rembrandt’s Among the newest equipment of with a three-dimensional solid body “Danaya,” which was examined after being interest may be the Raman system. Apart sensor, and the other is a Russian-made subjected to an acid attack (Figure 3). from the Raman-Fourier spectrometer, diffractometer equipped with a so-called X-ray imaging shows changes introduced this equipment also includes a Raman Gandolfi head. The technique is of interest by Rembrandt in his initial design. The microscope (a set with three lasers—green, not only for phase analysis, but it also hand and leg look different compared to red, and infrared) and two remote probes. brings new possibilities in distinguishing those in the final version.