MIGUEL BOYAYANChemical composition of the pigments helps to tell the story of the pictureMIGUEL BOYAYAN
At 8 o’clock in the morning of December 17 last year, a Saturday, a day on which the academic activities cease or diminish on the vast campus of the University of São Paulo, in the Butantã district of São Paulo, a car driven by a private chauffeur, and escorted by security guards, parked in front of the Physics Institute. Out from inside came restorer Marcia Rizzo, with a canvas 1 meter in width and 1.18 meters in height, which was rapidly taken to the premises of the Ion Beam Analysis of Materials Laboratory (Lamfi), where a team of researchers was waiting for it to start their work.
On that day, instead of supplying data for studies of air pollution or semiconductor or magnetic thin films, two of its main areas of work, the laboratory’s equipment and physicists were for hours on end at the service of an initiative to unveil a commonplace, but very interesting, kind of mystery, from the world of arts: the origin and, if possible, the authorship of a picture – in this case, a painting attributed by its owner, a private collector, to the Belgian Anthony van Dyck (1599-1641), a Flemish painter who gained fame in the first half of the 17th century for his portraits of kings and queens of Europe, in particular from the English court.
Lead white
With the assistance of a technique for emitting X-rays known as Pixe, which makes it possible to identify the chemical composition of a good deal of the pigments used in a painting without causing damage to the work of art, the scientists produced important information on how and when the canvas must have been done, and even in what way it was restored or modified in the course of its history.
They discovered, for example, that the white tones originally present in the picture, which shows the crucifixion of Jesus, comes from the so-called lead white, the pigment of this color most used by painters between antiquity and the end of the 18th century. The retouched white parts of the painting, like pieces of the cloth that covers Jesus’ waist, show another pigment, zinc white, which only began to be used from the 19th century onwards, and became the favorite with artists.
“For the while, the study of the pigments seems to indicate that it really is an old picture, and not contemporaneous”, explains Paulo Pascholati, one of the physicists who took part in the analyses. “But we cannot pinpoint the time, nor the identity of the painter.”
Significant quantities were also found of brown pigments, rich in manganese and commonly employed by painters who lived 400 years ago, like the brown of Van Dyck (bituminous earth plus iron and manganese), found in the hair of the soldier next to Jesus. There was also the expectation of catching in the painting a kind of blue pigment much valued during the Renaissance, ultramarine blue, a sulfur complex derived from an ornamental stone, lapis lazuli.
Although today it appears extremely darkened by the process of oxidation in its protective layer (or varnish), the mantle of the Virgin Mary, one of the personages of the picture, is blue in color – and the researchers thought that there could be ultramarine blue there. But they only found less noble forms of blue, perhaps an indication that the sponsor of the canvas, if there was one, did not invest much money in the work of art.
The painting portrays a classic scene of Christianity, the Calvary of Christ. Against a background much darkened by the action of time, the canvas shows the son of God crucified in the center, Mary Magdalene clutching his feet, St John the Evangelist and the Virgin Mary on one side, and a soldier, another person and a horse on the other. The picture that is a candidate to being by Van Dyck shows evidence that, in the course of its history, it underwent modifications, restorations and damages of all kinds. In the lower right corner, there is a tear.
The canvas changed frames several times, and was obliged to adapt to frameworks of different dimensions. It was also folded almost in the middle, leaving marks of this aggression close to Jesus’ right arm. And it shows two patches: pieces of cloth were cut and later fitted back into the painting. “The picture has also undergone what we call a selective cleaning”, claims Marcia Rizzo, for over 20 years a restorer and a student for a master’s degree in chemistry at USP. The picture’s original varnish – of the Dammar kind, the one most used by ancient painters, which has a characteristic of darkening too much with the passage of time – was removed only from certain parts of the picture, as in the figure of Christ.
Time and space
Nobody had the illusion that, in isolation, the study with the Pixe methodology was going to settle the central issue about the doubtful authorship of the picture. Technique does not work magic. Actually, with the new approach, what the researchers wanted was to provide more data that, added to the information achieved in other scientific and artistic analyses, may perhaps help to elucidate the mystery of the hands that painted the canvas. “The use of the knowledge from physics and chemistry to study the elements of a work of art does not provide definitive replies”, Marcia Rizzo ponders.
“It just helps to locate it in time and space.” Whenever there is a controversy about the authorship of a canvas or sculpture, the last word on its authenticity is up to scholars of the work of the great painters. Personally, Marcia believes that the canvas with the calvary of Christ is a work from the renaissance Flemish school and must be some 400 years old. But, whether it really is a Van Dyck, she does not risk saying. Some specialists in painting speculate that the picture has a style closer to that of the Flemish painter Jacob Jordaens (1593-1678), also born in Antwerp like Van Dyck, who worked on religious themes very frequently.
Standing for Particle Induced X-Ray Emission, the Pixe technique consists of exposing the object to be analyzed to a proton beam produced by a particle accelerator. The protons collide with the surface of the artifact ahead of them, more precisely with the atoms of the substances that make up the object under study, and return to the equipment in the form of X-rays characteristic of the chemical elements of the sample. Each element (iron, aluminum etc.) emits a specific radiation, a sort of signature in X-rays. Accordingly, the researchers manage to identify the chemical composition of the materials present in extremely small points of the sample, with a diameter of 1 or 2 micrometers.
Pixe shows a few advantages when compared with other nondestructive methods equally capable of providing the chemical composition of the materials: it does not need to be carried out in an environment under a vacuum, as happens in the studies produced with scanning electron microscopes, and gives results that are a bit more refined than those from X-Ray Fluorescence Spectroscopy (XRFS). “This last technique, though, can be used by a piece of equipment that is easy to transport and can be taken to museums”, says Manfredo Tabacniks, from Lamfi/USP.
“With Pixe, the object of the analysis has to be taken to the equipment.” In the case of the possible Flemish canvas, the scientists went so far as to choose 30 points for analysis, which covered the different pigments that bring color to the work of art, but they only had time to carry out the study on a little more than a dozen of them. Each point was bombarded by the atomic particles for about 20 minutes. The proton beam crosses through the varnish that protects the painting, reaches the layers of paint, and returns with the signatures in X-rays of the chemical elements that constitute the pigments used in the canvas. All this without causing the picture any damage.
It is not only pictures than can benefit from analyses by X-rays. Techniques like Pixe and XRFS are also useful for studying the constituent materials of sculptures. “Besides characterizing the alloy that makes up objects and statues, we can identify the compounds that cause corrosion and lead to the accumulation of deposits on the pieces”, claims physicist Márcia Rizzutto, who examined four items from the collection of USP’s Archeology and Ethnology Museum (MAE), with the assistance of both techniques.
Amongst the most remarkable results of the work, Márcia noticed that a statue from the museum’s African collection – an Edans, produced basically of an alloy of copper and zinc by the ancient Ogboni society – showed a very selective corrosion. The zinc element in its alloy was more attacked than the copper. This kind of detail is important for the museum managers, who have to be concerned with the conservation of their collection. In a project that is able to count on financing from FAPESP, Márcia also employs the techniques for characterizing teeth and archeological vestiges found in shell middens.
Hidden Da Vinci
In some great museums, like the Louvre in Paris, the use of increasingly refined methods for analyzing the physical or chemical properties of works of art has become commonplace in the last few decades. The conservation and restoration area of these temples of the plastic arts has equipment similar to that found in the best universities of Europe and of the United States. And those who do not have it frequently open their doors for scientists to carry out their measurements. With the assistance of science, a bit of luck and a lot of work, the specialists in painting and sculpture may discover details of the work of an author hitherto unknown. Even pictures that have been scrutinized extensively by the trained eyes of specialists in painting reveal unsuspected facets when submitted to new forms of analysis.
In July 2005, the curators of the National Gallery, in London, made public the information that, hidden beneath the layers of paint of the famous picture Madonna of the Rocks, by Leonardo da Vinci, there are two drawings done by the Renaissance master. The first shows the Virgin Mary in a different pose from the one that actually ended up being painted in the version of the canvas that is part of the collection of the English museum. This was an initial idea, a sketch that, for some reason, Da Vinci did not take forward. The second is the outline of final shapes of the scene that ended up immortalized in the work.
This hidden work of the painter only came to light because the Madonna of the Rocks was filmed using a complementary technique to infrared photography, the so-called infrared reflectography, which enhances drawings not visible to the eye located beneath a painting’s set of pigments. Reflectography is good for highlighting drawings in black done with a material rich in carbon, like graphite. “In Brazil, unfortunately, we use physical and chemical analyses very infrequently in studying art”, Pascholati. Works like the one carried out on the Van Dyke candidate picture are still exceptions.
The Project
Trace elements in biomaterials (nº 03/00311-4); Modality Regular Research Project Grant; Coordinator Márcia Rizzutto – IF/USP; Investment R$ 22,000.00 and US$ 5,000.00 (FAPESP)
