Silchenko T.N.
1. X-rays and painting
The day of Roentgen's discovery of a “new kind of rays” is considered to be November 8, 1895. Already the next year, Roentgen, using open rays, studied, along with other materials, various pigments. At the same time, some physicists were able to obtain the contours of the images in the painting from X-ray photographs. These were the first laboratory experiments; practical application for the study of X-ray patterns began at the end of the first quarter of the 20th century. and is gaining its due place among other methods of studying the material part of paintings only gradually and not without objections. Opinions have been expressed that the time and money spent on x-ray examinations are not worth the results they give, and that x-rays can harm the picture. The main reason for these and similar objections was the inability to fully use the results of the study and insufficient knowledge of the physicochemical properties of both X-rays and the picture itself. It has now been definitively established, both theoretically - based on a deep study of the nature of X-rays, and practically - based on careful experimental testing, that the dose of X-rays is even a million times greater than that which (on average) is needed to obtain an image from the picture, does not cause her any harm and cannot in any way affect her further existence. At first, the obstacles to the widespread introduction of the X-ray research method into museum practice were the imperfection of the necessary equipment, the high cost and complexity of its use, which required the participation of a small number of radiologists at that time. Nowadays, all these complications have disappeared, and only the inertia of museum workers can explain the fact that the most valuable research method has not yet entered into the daily practice of all Soviet museums and restoration workshops as firmly as it has entered medicine and other areas of science and technology. The study of paintings using X-rays is especially valuable if it is carried out in parallel with the study in ultraviolet rays (luminescent method), sometimes with the help of a binocular magnifying glass. Such a comprehensive study, revealing what is hidden inside the painting and what is not visible in ordinary light on its surface, provides the most valuable data about the material part of the painting, necessary not only for the restorer, but also for the art critic, artist and curator. Other methods, such as chemical analysis, can also be successfully used to study paintings, but they require special equipment and specialists; the need for such research arises in exceptional cases; their introduction into the daily practice of museum workers to the extent that it should be with X-ray and luminescent methods is less necessary; Therefore, this article deals only with these two methods.
Data on the nature of X-rays and their physical and chemical properties can be found not only in truly vast literature - scientific and popular, but also in any modern physics textbook. The technique of their practical use in various fields is described in detail in the relevant manuals, so this article very briefly presents the main provisions that are directly related to the practice of studying paintings.
The use of X-rays to study paintings is based on the fact that rays passing through a painting, under favorable conditions, produce an image on a fluorescent screen or a photograph on photographic film. Practice suggests using only photographs, and not transillumination, because: 1) with translucency it is impossible to catch, much less remember, all the smallest details that are recorded in the photographs; 2) when studying large paintings, it is technically difficult to use the screen; 3) transillumination is possible only in complete darkness, while the screen, hard and heavy (thanks to lead glass), must be pressed tightly against the picture, which can lead to damage to it; 4) an x-ray is an objective document, always ready for demonstration, comparison and comparison with a number of other photographs, and this is extremely important when studying both one painting and, in particular, a series of paintings, for example, when studying the technique of a particular master or school. Accumulating an archive of X-ray images of paintings is one of the most important tasks of every large museum.
According to the wave theory of light, X-rays are electromagnetic vibrations with wavelengths from 725 to 0.10 A°. 1 The properties of X-rays and, in particular, their penetrating ability largely depend on the wavelength: the shorter the waves, the greater the penetrating power of the rays, or, as they say, they are harder, and, conversely, the longer the waves, the less of them penetrating force - they are softer. The definition of “hard” and “soft” rays is arbitrary and does not sufficiently characterize the actual properties of a given beam of rays: soft for one purpose, they may be too hard for another. The designation in wavelengths has scientific meaning. In practice, when using tubes with a heated cathode, it is customary to determine the rigidity by kilovoltage, i.e., the voltage of the electric current that is supplied to the tube, since the wavelengths in the emitted beam change depending on it, and this determines the penetrating ability: the higher the kilovoltage, the harder the rays. The choice of one or another rigidity is determined by the transparency of the object under study for X-rays. For some clarification, we can say that to study various metal products, hard rays are required, to study the human body - medium rays, and to study paintings - soft rays (about 30 kilovolts). An X-ray beam consists of a mixture of rays of different wavelengths (similar to visible "white" light), with the shortest corresponding to the height of the applied kilovoltage, and the longest (when working with a conventional diagnostic tube) those produced at 15 kilovolts, since the rays softer ones are filtered out by the glass wall of the tube.
When a beam of rays passes through an object (for example, a painting), soft rays are delayed to a greater extent than hard rays, due to which not only a general quantitative attenuation occurs, but the ratio of soft and hard rays in the beam also changes towards a percentage increase in the number of hard rays . In practice, the intensity attenuation, i.e., the difference between the intensity of the rays with which they came out of the tube and the one with which they, having passed through the object being photographed, will affect the photographic film, depends on the chemical composition of the object and its thickness: the attenuation is proportional to 4- 1st degree of the element's serial number according to the periodic table and 3rd degree of wavelength; moreover, the attenuation increases rapidly with increasing thickness of the layer of material through which the rays pass, especially with soft rays.
In the picture, the difference in the thickness of various sections in most cases is not particularly large and the retention of X-rays when obtaining an image is affected to a lesser extent than the chemical composition of the materials from which it is constructed; for example, even a thick layer (on the scale of a painting) of ocher blocks X-rays much less than a thin layer of white lead or pure gold. This becomes clear if we take into account that the stopping power is determined not simply by the serial number of the element, but by its 4th power. For example, the ratio of the serial numbers of iron (26) and lead (82) will be only about 1:3, and the ratio of their 4 degrees will be about 1:110, also for zinc (30) and lead (82) their ratio is 4 -x powers will be approximately 1:56.
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calcium (20) and |
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silver (47) |
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gold (79) |
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(the table shows metals whose compounds are pigments, most often used in painting).
In order to determine how significantly a substance consisting of several elements will block X-rays (and all the materials from which the picture is built are exactly that), it would be necessary to calculate the sum of the blocking force of each element and its quantity. Of course, in the practice of studying paintings, such calculations do not have to be made, if only because the exact chemical composition of paints and their ratios in a particular area of the painting (when mixed or superimposed on each other) are not known. The above information is given only to show what properties of the materials from which the picture is constructed create the most favorable conditions for obtaining a clear, richly detailed x-ray image and what shooting technique should be used.
As an X-ray object, the painting has the following advantages over other objects: small thickness and flat surface; immobility, relative transparency for x-rays. Thanks to this, with the right technique, it is possible to obtain the maximum contrast and sharpness of the image for a given picture, because: 1) the effect of scattered rays is almost completely eliminated, as well as the “blurring” of the picture from the movement of the object at any exposure duration; 2) it is possible to ensure a tight and uniform fit of the film; 3) soft rays are used, which give the greatest contrast in the image. Unfavorable conditions are created if the painting is made with paints that block rays weaker than its base or primer, or that differ little from each other in transparency for X-rays. In most paintings, especially by old masters, the ground, due to the absence or small amount of lead paint in it, is quite transparent to X-rays.
Paints common in tempera and oil painting can practically (conditionally) be divided into four groups:
1. Organic (kraplak, black, for example soot).
2. Derivatives of metals with a low atomic number or with a small percentage of metal (ocher, etc.).
3. Derivatives of metals with average atomic numbers (zinc, copper).
4. Derivatives of heavy metals (lead, mercury).
For rays of the hardness that is used in the study of paintings and with the usual thickness of the paint layer, the first two groups, like the binder and coating varnishes, are completely passable for x-rays and on x-ray photographs they give areas of maximum density for a given image. Paints of the third group block the rays quite weakly and only with a sufficient layer thickness do they create an overall background of a photo of medium density (“gray”) without sharp boundaries, with weakly expressed chiaroscuro (halftones). Against this background, darker places appear with varying clarity, corresponding to areas of the picture made by the first or second group, and lighter, sometimes completely transparent, corresponding to details made with paints of the fourth group.
Lead white plays an extremely important role. Of all the paints, they block X-rays most significantly; Moreover, it is rare to find a painting that does not contain lead white, either in pure form or in the form of “bleaching,” that is, mixed with other paints (only in later paintings - from the beginning of the second quarter of the 19th century - lead white is sometimes partially or completely replaced by zinc). Therefore, the completeness of the image of a painting on an x-ray is determined almost exclusively by the amount and distribution of lead white on it. The painting technique also has a very great influence on the nature of the photograph (in the sense of image reproduction): with layer-by-layer painting, when the underpainting was first painted, with details in details and chiaroscuro, using lead white, and then covered with glazes, a reproduction of the picture is obtained on the x-ray photograph, close to a regular photograph (and sometimes even more detailed). With a single-layer technique, when the required color or shade is obtained by mixing colors on the palette, the picture may not produce clear contours and rich contrasts. This explains the important role of underpainting - it is on it that the completeness of the image in the photograph depends; glazes, usually made with a very thin layer and paints that are transparent to X-rays (and ordinary light), do not produce shadows on an X-ray photograph.
Let's take a closer look at several classic paintings and find out what secrets they really hide. Quite interesting, although some of these pictures are really scary.
Whale in Hendrik van Antonissen's "Beach Scene"
After a painting by a 17th-century Dutch artist ended up in a public museum, its owner noticed something unusual about it. Why are so many people suddenly on the beach for no apparent reason? While removing the first layer of the painting, the truth came out. In fact, the artist originally painted a whale carcass on the beach, which was later painted over. Scientists believe that it was painted over for aesthetic purposes. Not many people would want to have a painting of a dead whale in their home.
Hidden figure in Pablo Picasso's painting "The Old Guitarist"
Picasso had a very difficult period in his life when he did not even have money for new paintings, so he had to paint new paintings on top of the old ones, repainting them many times. This was the case with the old guitarist.
If you look at the picture very carefully, you can see the outlines of another person. X-rays showed that it had previously been a painting of a woman with a child in the countryside
The mysterious disappearance of the Roman king
The portrait "Jacques Marquet, Baron de Montbreton de Norvin" by an artist named Jean Auguste Dominique Ingres is one of the most prominent representatives of political pentimento. On this canvas you can see a portrait of the chief of police of Rome, but earlier something else was written on this canvas.
Scientists believe that after the conquest of Rome by Napoleon, this canvas featured a bust of Napoleon’s son, whom he himself proclaimed king of Rome. But after Napoleon was defeated, the bust of his son was successfully painted over
Dead baby or basket of potatoes?
You can see in the painting by the French artist Jean-François Millet called "L" Angelus" from 1859, two peasants who stand in the middle of a field and mournfully look at a basket of potatoes. However, when the painting was studied using X-rays, it turned out that before In place of the basket was a small coffin with a small child.
The X-ray was not taken by chance. Salvador Dali insisted on x-rays, claiming that the painting depicted a funeral scene. In the end, the Louvre reluctantly x-rayed the painting, and Salvador Dali's premonition was justified
The painting "Preparing the Bride" is not what it seems
The painting "Preparing the Bride" is actually an unfinished painting. This painting was part of a series depicting the traditions of French rural life by Gustave Courbet. It was painted in the mid-1800s and acquired by the museum in 1929.
In 1960, the painting was studied using X-rays and what scientists discovered shocked them. The painting originally depicted a funeral scene, and the woman in the center of the painting was dead.
Modern art historians are increasingly resorting to studying paintings by old masters using fluoroscopy, using the well-known property of lead white: to block x-rays. An X-ray image obtained by transilluminating a particular painting can show compositional changes made by the artist, alterations of individual details of the painting, corrected errors and other features of the artist’s technical process.
Using this method, it was established, for example, that the Dutch painter Rembrandt, when creating “Self-Portrait” in 1665, initially made a mistake by giving a mirror image of himself on the canvas: he had a brush in his left hand and a palette in his right. The artist noticed this only after the painting was completely finished. Having covered his hands with a thick layer of paint on the canvas, he painted them again. Now the brush was in the right hand, and the palette in the left.
Second example. The Flemish painter Rubens (1606-1669) changed the original composition of his painting "Portrait of Francesco Gonzaga" (kept in the Kunsthistorisches Museum in Vienna) after it was completed. Compositional changes are clearly visible in the above x-ray.
Also, quite recently, with the help of X-rays, it was possible to find out which of the two paintings by the artist Van Dyck “Saint Jerome and the Angel” (on the title of the article) is genuine, and which is just a copy (albeit an excellent one).
P.S. Perfume says: And when studying some old paintings, you can be surprised to discover that their paints contain the same components as maxilift cosmetics. Maybe this is the secret of the quality and durability of this cosmetics? By the way,
MUSEUM LABORATORY Laboratoire de musee. A service that conducts scientific, physical and chemical analyzes of paintings.
A museum laboratory should not be confused with a restoration workshop, with which they are in more or less close contact, depending on the country and institution. The results obtained by scientific methods make an important contribution to the knowledge of a work of art; they make it possible to accurately analyze the material side of a painting, which is so necessary both for storing a work of art and for the history of painting techniques. Scientific photography, radiography and microchemical analysis (we name only frequently used methods) seem to reveal the secret life of a painting and the stages of its creation, making visible the first sketch, registration and subsequent changes; they provide the necessary information to restorers, connoisseurs, historians and art critics.
Story
In France, the interest of scientists in the preservation and study of painting arose in the second half of the 18th century. among encyclopedists. The physicist Alexandre Charles (1746-1822), whose laboratory was located in the Louvre in 1780, was. probably one of the first scientists who tried to study the preservation and technique of the painting using optical instruments. In the 19th century Chaptal, Geoffroy Saint-Hilaire, Vauquelin, Chevrel and Louis Pasteur, in turn, devoted their research to the analysis of the components of paintings.
In England, the scientist Sir Humphry Davy (1778-1J29) also tried to analyze paintings and their constituent substances. In the second half of the 19th century. German scientists also became interested in these problems. The first research laboratory was created in 1888 at the Berlin Museum. Seven years later, the physicist Roentgen attempted to make the first x-ray photograph of the painting. At the beginning of the 20th century. the chemical method was improved, and in France, scientific work was resumed in the Louvre in 1919. However, it was only after the first international conference, which took place in 1930 in Rome, that the world witnessed the true beginning of scientific work. Among the services that existed by that time, mention should be made of the laboratory of the British Museum (established in 1919), the Louvre and Cairo Museum (1925), the Fogg Art Museum in Cambridge (1927) and the Museum of Fine Arts in Boston (1930).
Somewhat later, laboratories were created at national or municipal museums: the Central Laboratory of the Museums of Belgium (1934), the Max Dorner Institute in Munich (1934), the laboratory of the London National. gal. and the Courtauld Institute (1935), the Central Institute for Restoration in Rome (1941). Since 1946, similar services have existed in most major museums in the world in Poland, Russia, Japan, Canada, India, Sweden, and Norway; other laboratories are still being created.
Scientific methods
Optical research, expanding the capabilities of vision, allows us to perceive what was previously barely noticeable or completely invisible. Nevertheless, studying a painting in natural light is a necessary preliminary stage of laboratory research, as is photographic recording. Traditional methods of photography have recently been supplemented with our own technologies for the scientific study of paintings. Light falling tangentially. A painting placed in a dark room is illuminated by a beam of light parallel to its surface or forming a very small angle with it. By changing the position of the light source, you can highlight different sides of the painting surface. Visual inspection and photographic recording of the painting from this angle indicate, first of all, the safety of the work, and also allow us to determine the artist’s technique.
It should be noted, however, that such a view of the picture distorts reality, and therefore the understanding of the information received must be accompanied by an analysis of the original.
Monochromatic sodium light. In this case, the picture is illuminated by 1000 W lamps, emitting only yellow light located in a narrow band of the spectrum. This results in a monochromatic appearance of the work being examined, which reduces the color impact on the retina and allows for an accurate reading of the lines. Monochromatic light removes the effect of foundation varnishes and allows you to read otherwise invisible inscriptions and signatures. You can also see the preparatory drawing, provided that it is not hidden by too thick a layer of glaze. The results obtained are less rich in data than those provided by infrared radiation, but the advantage of this method is that it can be used in visual analysis of the picture.
Infrared radiation. Thanks to the discovery of infrared radiation, it became possible to photograph what seemed invisible, but the results of this analysis can only be perceived by the human eye with the help of a photographic plate. Infrared rays reveal the previously unnoticed state of a work of art by absorbing or reflecting the color matter that makes up the painting. A photograph reveals to us an inscription, a drawing, an unfinished stage of work that is invisible to the eye. However, the results are unpredictable, and deciphering the image obtained in a photograph is often very complex and difficult. Nevertheless, it becomes possible to read the inscriptions sometimes located on the reverse side of the painting. In addition, infrared radiation makes it easier to determine the nature of the pigment, complementing the results of observations made under a microscope or physicochemical method.
Ultraviolet radiation. Under the influence of ultraviolet rays, many substances that make up the painting emit only their inherent glow; The results of this analysis can be photographed. The phenomenon of fluorescence is not only a consequence of the chemical composition of the dyes, but also depends on their age, which can lead to a difference in the colloidal state. The use of ultraviolet rays is of great interest not so much for the history of art itself, but for determining the safety of paintings. Old varnish coatings in ultraviolet radiation appear as a milky-colored surface, on which later registrations appear in the form of darker spots. Deciphering the obtained data is not easy and most often requires additional microscopic analysis of the surface, which will confirm or refute the hypothesis about the rewritten place, about the removal of varnish, or about traces of these damages, which are often very difficult to determine from photographs. However, this method is necessary for the restorer and allows him to assess the extent of previous restorations.
Macro and microphotography. These are photographic techniques often used when examining paintings. Macro photography magnifies the visible image (the magnification scale is very rarely greater than 10x) using a short focal length lens. It can be carried out in natural light, as well as in various lighting (monochromatic, ultraviolet, tangential). It allows you to isolate certain parts of the picture from their context and draw attention to these details. A microphotography is an image of a fragment of a painting obtained using a microscope. It records changes, invisible to the eye, in the state of a small area of the picture plane, sometimes not exceeding several tens of square millimeters. It also allows you to observe the condition of the varnish layers, the distinctive features of craquelure and pigments.
Microsections. This method is similar to that used in medicine for histological sections. Here, polyester resin is used to coat the test sample. After adding a small amount of catalyst and accelerator, the monomer polymerizes at normal temperature. The result is a solid and transparent mass, similar to glass. This mass is cut in such a way as to obtain a cut in a plane perpendicular to the plane of the paint layers; The flat section is then polished using aluminum oxide in the form of an aqueous suspension as the grinding material. The production of cross sections has been mentioned in various works over the past sixty years.
Electron microprobe. Its use solves several problems at once. This method, which satisfies the size criterion (micrometer) and allows an accurate analysis, can be used, in particular, when studying sections of a painting; a polished surface or thin section; an electron beam of light can examine layers of different composition, the thickness of which is several micrometers, and the elements mechanically inseparable. Inside each layer, a microprobe allows one to determine the elements that make up each material, and the resolution of this method far exceeds that of the best optical instruments.
Radiography. X-rays were first discovered in 1895 by the physicist Roentgen, who a few years later in Munich made the first X-ray photograph of the painting. In France, similar experiments were carried out only during the First World War, in 1915, by Dr. Ledoux-Lebard and his assistant Gulina. The work was continued at the Louvre in 1919 by Dr. Cheron. Systematic research began in museums only a few years later: in the Louvre - in 1924 (Celier and Gulina), a little later at the Fogg Art Museum (Burrows), in England (Christian Walters) and Portugal (Santos). After World War II, radiography became the most commonly used method of analysis.
Laboratories use weak X-rays. Generators are most often anti-cathode tungsten lamps, similar to those used in medicine. There are also devices for very weak radiation with lamps with a beryllium window and water cooling. The X-ray films are placed in a black paper envelope and can come into contact with the painting without risk. The clarity of the resulting image depends in part on the degree of contact of the film with the surface of the painting. X-rays recreate the invisible appearance of the painting. However, if the base of the painting is thick and the ground is of high density, then the internal structure of the picture may be difficult to read, but if radiation passes through the canvas and ground easily, then the paints used for the preparatory drawing, usually on the base, are easily revealed and thus the state of the picture, invisible to the eye, is revived , a stage of creativity previously inaccessible to perception. The first stage of work is not always visible on an x-ray. So, for example, in the photograph of E. Lesueur’s painting “Muses,” a complex combination of the first and second stages of work is revealed; the face is visible simultaneously in profile and from the front. If, on the contrary, the picture was painted with colors of low intensity and then covered with wide glazes, we will not see this first stage at all. The painting is subjected to X-ray analysis in order to infer the condition of the painting in anticipation of restoration or for purposes of interest to art historians. But the most accurate results from radiography can be expected in determining the composition and condition of the base.
The basis. The base is a wooden or copper board or canvas on which a layer of paint is applied. When it is necessary to examine a painting painted on copper, which, however, is rare, radiography cannot help, since the weak X-rays used in the analysis are not able to pass through the metal. However, if rays of greater penetrating power are used, they will not provide any information about the paint layer itself. In this case, only a study of the picture in infrared and ultraviolet rays can bring some clarity. When we are talking about a painting painted on wood (and there were a majority of such paintings before the 17th century), studying the properties and structure of the wooden base, visual inspection of which is often difficult, can be extremely useful. The wooden base is hidden on one side with a layer of paint, and the artist himself sometimes covers the other side with primer to avoid moisture. This primer is usually one-color or marbled. When the paint layers and soil are permeable to X-rays, an X-ray image of the wood base can be obtained.
Radiography makes it possible to trace the results of actions performed on a painting and to detect the technical means and techniques used by primitive artists. Thus, in an x-ray photograph you can see pieces of rough canvas included in the ground so that the joints of the boards do not appear on the paint layer itself. Raw fiber mixed with lime mortar is used in many 14th century paintings. In the 17th and 18th centuries. paintings, as a rule, were painted on canvas, which was then duplicated, that is, additionally reinforced with another canvas; this canvas (usually late 18th or 19th century) does not allow the original support to be seen. Duplicated canvas, provided that it was not impregnated with white during priming, does not pose a particular problem for X-rays.
The characteristics of the canvas depend on the country and era where and when the work was created. Thus, Venetian canvases most often have a woven pattern; Rembrandt used simple canvases. Thanks to x-rays, all tissue features can be determined. X-rays detect not only the type of canvas, but also the inserts in them. An x-ray allows you to assess the extent of changes (extraordinary or cropped pictures).
paint layer. X-ray examination of the paint layer of a painting allows us to solve some problems of its preservation. Derelict areas often occupy a much larger area than those in need of restoration. Thus, to hide a loss of several square millimeters in area, recordings of several square centimeters are often made. By comparing an ultraviolet photo showing the records and an x-ray showing the loss itself, it can be determined whether the replacement area accurately covers the loss. It should be noted that on an x-ray, the loss of the ink layer appears black or white. If they are covered with a thin layer of paint, they will be darkened, and the structure of the canvas or the wooden base of the painting will be clearly perceived.
On the contrary, when the losses are sealed with mastic, they will not let the rays through and form a white zone. Losses are also revealed by the appearance of areas where the canvas appears more clearly than in the rest of the picture. In addition, radiography allows you to study the main elements of the painting from the point of view of art history and technical techniques. In order for the painting to be visible, it is necessary to expose the soil, which is located between the base and the paint layer, to X-rays. In most cases, the wooden or canvas bases of paintings are permeable, with the exception of those that are reinforced on the reverse side. Whitewash, which is often included in artists' palettes, is made from heavy metal salts; Lead white creates a barrier to X-rays. Black paints, on the contrary, have very low density. Between these two extremes are colors that vary in intensity, which is why the X-ray image is subtly nuanced.
When the preparatory drawing is executed in the grisaille technique, consisting mainly of white, sometimes tinted, very interesting x-ray photographs can be obtained. If the preparatory drawing is painted with low-density paints, it is almost invisible; Only the general composition of the picture is visible.
When a painting is painted with glazes, the image, although visible, is not of contrast; this is the case with some paintings by Leonardo da Vinci. Many artists have used techniques that fall between these extremes. When the artist remade the painting, rewrote some of its parts in order to give them a finished form, different from the original (it was discovered by X-rays), then they talk about registrations (see). Registrations are very different. Some almost repeat and refine the original lines, and this is the most common case.
In the XIII-XVI centuries. artists usually executed their canvases only after they had worked out the preparatory drawing with exceptional precision, and therefore very few discrepancies between the preparatory drawing and the completed painting are found. At the same time, these artists worked with paints with a fairly low density - X-ray photographs most often have barely any contrast. X-rays are intended to be of great assistance in studying the style and manner of an artist. If x-rays of paintings by the same artist reveal the artist's consistency in the choice of pigments and brushes and in the form of strokes, then erroneous attributions can be corrected, chronology can be clarified, and forgeries can be detected. By fakes we mean only those paintings that are executed in order to mislead. Fakes should not be mixed with copies or old replicas, which should only be correctly attributed. But counterfeit elements that are present in the original painting itself (fake craquelure, signatures) can be detected using radiography, because the copyist and forger strives to reproduce only the surface of the works he imitates.
Microchemical and physicochemical analysis. To the mentioned methods, often used in museum laboratories (since they have the advantage of not destroying the painting), one should add microchemical methods, which make it possible to establish the constituent elements of the painting based on a microsample. It is known that paint consists mainly of pigment dissolved in a binder or solvent. Microchemical analysis of pigments, mineral or organic, falls within the purview of traditional microchemistry when it comes to mineral substances. In addition, it uses infrared spectrography and chromatography for some organic pigments.
The binder is analyzed in a similar way. Infrared spectrography is also used for the analysis of natural resins, and chromatography for the isolation of aqueous solvents (gum, glue, casein). Chromatography in the gaseous state is used to separate the constituents of various fatty acids (oil, egg). Among the methods used in museum laboratories are diffraction and x-ray fluorescence, which, in comparison with the above methods, make it possible to obtain more accurate data regarding the nature and structure of the various mineral components of easel and wall paintings. X-ray fluorescence is based on analysis of the emission spectrum in the X-ray region. The sources can be a stream of electrons, a radioactive source, or a beam of X-rays. X-ray spectrometry is used in both physical and chemical aspects. But the instruments used today are not designed for direct analysis of bulky or very small objects. In addition, most of them have low sensitivity to elements such as copper, zinc, nickel and iron, due to the “background noise” produced by the equipment itself.
X-ray microfluorescence, developed at the Laboratory of Scientific Research of French Museums, was created taking into account all the specifics of museology. Its parameters are located between the parameters of an electron microprobe and a conventional X-ray fluorescence spectrometer. Its advantages are that it allows research to be carried out directly on the painting without destroying it, that the sample can be reused for another analysis and that it does not require pre-treatment of the sample; it is extremely reliable, very sensitive, and relatively simple. All these methods require special equipment and personnel.
There are only a few museums and national services in the world capable of carrying out this type of research; although, of course, as years pass, the traditional criteria for analyzing paintings will change under the influence of scientific advances, which should lead to a deeper knowledge of painting.
Application of methods. Preservation and restoration
Analysis of the materials from which paintings are composed, knowledge of the laws that determine the interaction of these materials with each other, on the one hand, and with the environment, on the other hand, contribute to the best preservation of paintings; scientific methods make it possible to measure and analyze the influence of external factors - light and climate on their safety. The degree of illumination greatly affects the properties of the painting. The museum laboratory has measuring instruments that allow you to select the lighting that best meets the requirements for the preservation of paintings. Some government (AFNOR) or international (1СОМ) organizations disseminate scientific developments in this area.
But most of all, museum curators insist on a climate and humidity favorable for paintings. Research to date has proven the key role of humidity. Sudden changes in temperature lead to changes in humidity and are considered destructive. Central heating, which dries out moisture, is also a negative factor for painting. The study of air pollution and its impact on the preservation of paintings is also the object of research in France and other countries. But museum laboratories must engage in scientific research on the paintings themselves. Using the methods listed above, you can detect damage to the base, swelling of the paint layer, and the interaction of pigments and binders. After laboratory testing to accurately determine the size of the damage, restoration can be carried out.
Expertise
The expert, like a doctor, supplements the visual examination of the picture with information obtained from scientific research. Thanks to microscopes, you can recognize fake craquelure and distinguish old pigments from modern ones. X-rays and infrared rays reveal the invisible state of a work of art, which the copyist or forger could neither comprehend nor reproduce.
Dating
Dating of the elements that make up the pictorial material is carried out in several laboratories in the United States, France and Germany. There are four methods for this that are still at the experimental stage. Work recently undertaken by the Mellon Institute in the United States makes it possible to date paintings using carbon 14, which identifies older fakes (less than a hundred years old). Indeed, since the beginning of the 20th century. The percentage of carbon 14 in the biosphere has changed, and its concentration has doubled from 1900 to the present day. The difference between modern oil and ancient oil can also be established on relatively small test samples (30 mg) using miniature counters. Lead white is one of the most commonly used pigments. Measuring the isotopic ratio of the lead contained in the pigment can be very accurate and can help answer the question of where and when the painting was executed.
Two other dating methods are still in the experimental realm; they are based on the activation by neutrons of foreign impurities contained in lead white and on the natural radioactivity of lead. But scientific methods are especially important for a deeper knowledge of painting itself. Physical and optical techniques reveal the stages of the creative process and recreate the characteristic features of the artist's technique: rubbing of paints, soil analysis, brush width, position of light - all this is very important for the art historian. Science is called upon to improve traditional methods of historical study and preservation of works of art.
--What is the method used to study the paintings of the classics?
— The basic principles of our approach are not new - this is X-ray fluorescence analysis (XRF), it is about 100 years old. It allows you to determine the elemental composition of the sample at a qualitative level. More advanced XRF technologies make it possible to quantify the content of elements in the object under study. About 20 years ago, XRF was used to quantitatively analyze the distribution of elements over the area of a sample—in this case, a painting, a work of art. (One of the first radiographically “rediscovered” paintings was Raphael’s “Lady with a Unicorn,” approx. "Newspapers.Ru".) We applied this method to study paintings by old masters and created special equipment that allows us to examine such large objects.
— How does XRF work to study paintings?
— The sample is examined by shining a focused beam of X-rays into the sample, point by point. The atoms in this extremely small region are excited by the primary beam. As a result of electron transitions between different energy levels, the sample fluoresces, and the emission parameters are characteristic, that is, unique for each element. Thus,
Based on the wavelength of the radiation, the dyes used to apply the image can be determined with a high degree of probability.
The fluorescent emission intensity for each element is visualized as a black-and-white distribution across the image.
Thus, our method is fundamentally different from classical radiography (transmission). If in radiography the radiation passing through a sample gives only a picture of contrast, our method - it can be called color radiography - records the entire emission spectrum of each individual element.
—What do “layers under layers” look like?
— The illustrations show the results of visualizing the hidden pictorial layers of several historical paintings; using them we can evaluate the capabilities of our method.
The first set of images is dedicated to the painting “Pauline im weißen Kleid vor sommerlicher Baumlandschaft” (Pauline in a white dress against the backdrop of a summer forest landscape). This painting is attributed to the brush of Phillip Otto Runge (a German romantic artist who lived 1777-1810). However, this opinion is not officially recognized, and a number of experts refute this assumption.
The picture was studied at the DORIS III synchrotron radiation source at the DESY (Deutsches Elektronen Synchrotron) research center in Hamburg (Germany). As a result, it was possible to separate the contributions of cobalt (Co, included in the paint “cobalt blue”), mercury (Hg, included in red cinnabar), antimony (Sb, included in the paint “Neapolitan yellow”) and lead (Pb, included in composition of lead white). The result of the contributions of each paint in black and white is shown in the illustrations.
They clearly show how
Our method visualizes the hidden layers of the painting: as you can see, the woman in the portrait originally had blond hair with ribbons woven into it.
Their color was approximately similar to the color of the belt. We don't see this in the final image - it's a direct result of seeing the layers underneath the layers. The findings were published in the journal Zeitschrift fur Kunsttechnologie und Konservierung (a bilingual German-American art research journal).
— What secrets are hidden in the depths of the paintings?
— The most striking example is the painting of the great post-impressionist Vincent van Gogh “A Patch of Grass” from the collection of the Kröller-Müller Museum (in the illustration for the note). Her X-ray fluorescence examination showed that under the paint layer on the canvas there was a portrait of a woman.
Van Gogh often painted his paintings on old used canvases. A visual examination of the “Patch of Grass” only made it possible to notice the outline of a human head - and nothing more. Our research allows us to see a second picture in the distribution of yellow paint. The results of the work were published in the journal Journal of Analytical Atomic Spectrometry.
— What is the importance of such research for art historians?
— Of great interest is the artist’s technique and the process of creating the work. And the underpainting remaining in the lower layers of the painting is not visible to the eye. However, it is the first and one of the most important steps in creating a painting. This is the draft that guided the artist through the entire creative process. The Old Masters used underpainting to sketch out light, shadows and outlines.
Observing the hidden layers of the painting gives us the opportunity to “peek” at what the original intention of the author of the work was.
Looking at the final result, it is almost impossible to judge such things.
— What paintings have already been studied using this method?
— The objects of the study were the works of Rembrandt Harmensz van Rijn, da Caravaggio, Peter Paul Rubens and other old masters of the 17th century.
— What practical benefits can this work bring?
“Using XRF, we hope to clarify the authorship of some works - either to dispel doubts about their origin, or to confirm that the paintings do not belong to the brush of the master to whom they are attributed. In general, this is a great chance to show that the world of art can interact with the world of chemistry. In general, chemistry is a comprehensive science. It's great to be able to show that chemistry is not just the science of molecules and reactions, but also the study of such beautiful works of art.
