I’d like a detailed notes on this please. It should be a comprehensive and in-depth analysis. Please use a tone and words that are simple and easy to understand. Include a mix of narrative summary and fully fleshed-out bullet point sentences, ensuring that every detail is explained clearly and makes sense. I don’t want any details removed or overly summarized; everything should be explained thoroughly. Provide details, give explanations, clarifications, make sense of everything. Do headings, subheadings, bullet points sentences, bullet points within bullet points, etc. Provide a markdown file of it as well.

Examining the Techniques
and Materials of Paintings . . .
Rustin S. Levenson
. . .
Rustin Levenson, a conservator, describes the various physical layers of a work as well as methods of scientific testing currently in use.—rds
. . .
Rustin Levenson is a painting conservator with private studios in New York and Miami. She has been on the painting conservation staff at the National Gallery of Canada and the Metropolitan Museum of Art, and has written numerous articles for conservation publications. In 2000, she co-authored Seeing Through Paintings: Physical Examination in Art Historical Studies, a comprehensive study of conservation issues directed to art historians.
. . .
Conservation treatments require spending large amounts of time with paint-ings. After weeks of hands-on consolidating, cleaning, structural treatment, and inpainting, a conservator develops an intimate sense of an artist’s work. The instincts acquired through this connection constitute a conservator’s pri-mary tool in the analysis of a painting.
Beyond the experienced eye, how does a conservator go about assessing the physical evidence of a painting? The arrival of a painting in the conser-vation studio unleashes a cascade of questions relating to the physical mate-rials and the state of the work.How did the artist achieve the effects of color, light, space, and surface? Has the age or condition of the painting changed these effects? Are the materials consistent with the date of the painting?
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Beginning to Gather Evidence:A Visual Examination
A conservator’s examination starts with removing the painting from the frame and using different types of light to study the work. Strong direct light is a good beginning.
Variations in texture and color that can indicate previous repairs or pen-timenti (the artist’s changes in design) are often visible in good light. Using transmitted light—holding the painting up to a light source and letting the light shine through—enables a conservator to examine cracks and damages. Raking light, which sweeps across the painting at an angle, facilitates a com-parison of the pattern of the paint impasto (the brush stroke) against that of the final design. Pentimenti are often first identified by impasto textures that reveal an earlier variation of the composition. Specular, or reflected, light al-lows the conservator to check the uniformity of the surface gloss and to gather knowledge about the varnish application and removal.
During visual examination, a conservator considers the layers that make up a painting. The support is the structural element, usually a canvas or a panel, that carries the ground,paint, and varnish layers.The ground or prepa-ration is the material applied to the support to give the texture and ab-sorbency needed for the application of the paint. The paint or design layer, applied over the ground, is where the artist carries out the visual idea.The fi-nal layer is a varnish coating, applied over the paint, which saturates the col-ors and protects the surface of the work. As these layers are examined, more questions are raised.
The Support Layer
The choice of support and its condition have a profound effect on the look of the paint layer.Various supports have been used throughout the history of Western art. Artists primarily used wood panel supports until the Renais-sance, when textile supports began to be employed. Copper supports were used occasionally by painters after the sixteenth century.
Comparing the support layer against those in other works by the artist can yield important information, from an approximate date to a determination that the composition has (or has not) been reduced, enlarged, or otherwise altered.
Wood panel supports vary considerably. The conservator first looks at a panel to see what type of wood was used. Reference books and articles sup-ply essential data about the woods utilized by various artists. For example, Jacqueline Marette, in her book Connaissance des primitifs par l’étude de bois,out-lines the types of wood used in European panels through the sixteenth cen-
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tury. She finds that,with minor exceptions in Spain,most painters used wood from local forests.1 Another article documents a wood support invented in the nineteenth century. On June 29, 1880, E. F. French of New York patented a board “built up of three layers of veneers with [the grain] crossing at right an-gles.” When this early plywood was discovered supporting George Iness’s Al-bano, Italy, it forced a reconsideration of the chronology of the artist’s oeuvre. Long assigned a date of 1874—six years before the plywood support came on the market—the painting had to be reassessed as part of Inness’s later oeuvre.2
Dendrochronology, the study of seasonal growth rings in trees, can be use-ful in dating panel paintings. If the appropriate rings are present in a panel, the date for the felling of the tree can be determined.However, panels do not always contain the rings necessary for such an analysis. Furthermore, it should be noted that the felling of the tree could considerably predate the use of the panel and that a forger could work on an antique panel.
Conservators ask many other questions as they examine a panel.Was the wood hand-primed or commercially prepared by a nineteenth-century col-orist? Has the wood been cut down? Was a hand tool or an electric tool used in making any visible cuts? Manual saws will make characteristically uneven marks, while the marks left by a machine saw are very regular. Machine saw marks on a painting dated before the Industrial Revolution indicate that the format of the support has been altered or that the painting was produced at a later date.
The characteristics of the woodworking on a panel, such as joins or other carpentry details, also can offer clues about a painting’s provenance because such details vary from region to region and from century to century.The ad-dition of a “cradle” is equally informative. A cradle is a wooden lattice at-tached to the back of a panel, usually by a restorer attempting to repair a split or to reduce warping.The woodworking of the mobile cradles on the reverse of three Raphael paintings in the Prado Museum, for example, is similar to that on seventeenth-century Spanish furniture. It is therefore reasonable to assume that the Raphaels were in Spain by this date. Later, during the Napo-leonic Wars, they were appropriated by French troops and sent to France.Al-though they were subsequently returned, the determination that the cradles are Spanish woodworking of the seventeenth century verifies that no support structures were added during the paintings’ sojourn in France.3
Textiles came into regular use as supports for easel paintings around 1500. The primary advantage of fabric supports was summarized by Giorgio Vasari in his famous sixteenth-century Lives of the Painters: “In order to be able to convey pictures from one place to another men have invented the convenient method of painting on canvas, which is of little weight, and when rolled up is easy to transport.”4
If a painting is on canvas, a conservator will note the type of weave, the
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presence or absence of seams, and the quality of the canvas. Claude Monet characteristically used a handkerchief-fine linen as opposed to the inexpensive bast fiber canvases that often supported the Tahitian paintings of Paul Gau-guin.A painting on a fabric that is unusual for an artist indicates the need for further research on the painting. Sometimes the textile support is merely an expedient piece of fabric—the red-checked tablecloth used by Vincent van Gogh in Large Plane Trees (Cleveland Museum of Art) or the serape used by Rufino Tamayo in Pueblo (University of California at Berkeley Art Museum).
Was the canvas stretched by the artist, his studio, or a professional colorist? If the support material was commercially purchased, is there a label or stamp to identify the maker? There are long bibliographies in the literature that out-line the types of supports selected by artists of various eras, and that locate and date identifying makers’ information. For example, a maker’s mark that in-cludes the address of a New York colorist can date a canvas quite precisely, since the stamped address can be matched to those recorded in historic busi-ness directories.5
If a painting is on canvas, it is important to examine the tacking margins. Are they original? If so, are the nails new or old? Is there more than one set of nail holes? Is there ground or paint on the tacking margins? Is the canvas brittle and aged at these points, or fresh and flexible? Are thread distortions resembling garlands visible next to the fold of the tacking margins? These arcing distortions are formed when a painting is stretched and prepared. Physics dictates that such scalloping should be nearly equal on opposing sides. A canvas with unequal distortions almost certainly has been cut down.
An examination of the stretcher design can play an essential role in dat-ing the work or determining its origin. Is the woodworking in the corner join specific to a certain era or country? Are there keys or wedges for ex-panding the stretcher in the corners? Many corner designs were patented and thus are datable.6
The Ground Layer
The ground, or preparation, layer is usually not visible to the viewer except along the edges or in areas of paint loss. Examining these areas, the conser-vator tries to assess the color, texture, and composition of the ground layer. Has the color of the ground affected the look of the paint layer? Has the composition of the ground led to condition problems? Is the ground in keep-ing with the purported date of the painting? Is underdrawing or incising vis-ible? Artists often laid out their designs on the preparation layer with chalk, ink, or paint. Some artists physically scratched the ground to lay out per-spective or to outline architectural elements.
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The physical evidence of a particular artist’s preparation and planning process can be decisive in the process of authentication and attribution.
The Paint Layer
The paint or design layer is where the artist executes the design and is a pri-mary factor in authenticating a work. In the paint layer, the binding medium —the liquid substance mixed with the powdered pigments—fixes the pig-ments to the ground and support layers.The choice of medium and pigments affects the application and aging properties of the paint. The ingredients in a painting medium vary according to the pigments and painting method.For example, a glazing layer would probably have resinous varnish added. If this quicker-drying layer is applied over a layer that is not yet dry, “alligator” cracking can occur. Pigments that fade or change can alter the appearance of a painting completely. The study of artists’materials has provided dates for the introduction of specific pigments into artistic palettes.7 A famous exam-ple of pigment identification in art history involves the story of Hans van Meegeren, a twentieth-century forger of Vermeer whose fakes were for a long time accepted as authentic Vermeers.Van Meegeren had foreseen that there might be technical analysis of his works, and carefully purchased natu-ral ultramarine, a pigment in use since ancient times, to paint the blues. His supplier, however, adulterated the ultramarine with cobalt blue, a nineteenth-century pigment, thus eventually confirming the forgery.8
As a paint layer becomes aged and brittle, and the canvas or panel beneath continues to move microscopically in response to atmospheric conditions, cracks form. Spike Bucklow has categorized these cracks using a precise set of descriptive terms. He was further able to associate craquelure patterns with different eras of art history.9 Patterns of cracking can also announce events in a painting’s past.A series of long, vertical cracks indicates that a canvas may have been rolled at some point. Concentric webs of craquelure indicate past blows or stress to a paint layer. A conservator will examine the pattern of craquelure to ascertain if it is in keeping with the materials used. Is it con-sistent with the support material, the artist’s materials, and the history of the work? Paint that crosses or covers craquelure patterns, for example, has been applied after the artist completed the painting and aging occurred. On the other hand, the total absence of cracks in a paint layer on an older panel or canvas should certainly raise some questions.
Observing and comparing the opacity and gloss of the paint layer can help locate retouches or overpainting. In one case, a Manhattan bank looked for-ward to displaying an eighteenth-century capriccio—an imaginary view of architecture in a picturesque setting—in its boardroom.A large glossy area in
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the foreground indicated the presence of overpainting.While testing this area in our studio,we found the artist’s original paint beneath.Removal of the var-nish and overpainting revealed a group of figures clustered around a bare-breasted Lucretia bleeding from her famous self-inflicted wound.Reclaiming the design of the artist certainly increased the authenticity of the painting,but decidedly reduced its boardroom appeal.
Because of the chemistry of the oil medium,paint becomes more transpar-ent with age, revealing pentimenti once successfully covered. These emerging shadows speak of the history of the painting and of the artist’s creative process. Some artists exhibit a sureness of conception that makes pentimenti rare in their works.Others are known for changing a painting significantly during the act of creation.An original by such an artist would be expected to show pen-timenti, while a copy would have few if any compositional alterations.
The Varnish Layer
The varnish, applied over the paint layer as a saturating and protective surface, can also have a profound effect on the look of the painting. Has the varnish discolored? Is the gloss uneven? Has it been partially or completely removed in the past? Is there a pattern on the reverse of the canvas that reflects the craquelure of the painting? When a painting is cleaned or varnished, the liq-uefied resin seeps through the cracks and stains the canvas. Such stains give an indication that the work had been treated after it had aged and cracked.
Technical and Material History
The body of information about artists’ materials and techniques has grown enormously since Cennino Cennini’s Il libro dell’arte, which described the artist’s craft in Padua in the late fourteenth century. In 2000,my colleague An-drea Kirsh and I published Seeing Through Paintings:Physical Examination in Art Historical Studies. The book details the investigation of paintings as physical objects.Using examples from the fourteenth through the twentieth centuries, we studied the historical and critical implications of the materials used by artists. The case studies demonstrate how physical evidence from all the lay-ers of the painting can be used to arrive at art historical conclusions.The an-notated bibliography presents extensive information on literature relating to artists and their materials and techniques. However, as the examples in the book illustrate, even with all the bibliographic references in the library, the material information in each painting must be carefully assessed before any conclusions are drawn.
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Anyone who has ever visited an artist’s studio and seen supplies piled up or shelved at random will understand how even artists themselves can be mis-taken about the materials used on a specific painting.Artists also experiment, lend materials, and purchase low-budget goods. It should further be noted that artists’ materials were subject to adulteration by unscrupulous suppliers and manufacturers. Besides the notorious case of Van Meegeren’s supplier, exam-ples abound of pigments and media altered for market in the eighteenth and nineteenth centuries.10 Results that are surprising in the laboratory would have been more surprising to the artists, who had obtained the materials in good faith.
Furthermore, there are very few museum artifacts that have remained un-touched by restorers, framers,owners,or other artists.The interjection of new materials into the work of an earlier era can convey misleading results, espe-cially on tests that rely on microscopic samples. For example, if a sample for pigment analysis is taken from a twentieth-century retouch in a seventeenth-century painting, the results could be very confusing. Information obtained from materials testing is only as useful as the sample is representative.
Condition
At the same time the conservator inventories the materials and techniques of the artist, the condition of the painting is assessed. Is the work stable? If there are repairs or overpainting, in what order were they carried out? Is there structural treatment or lining evident? Why was it done? What is the age of the treatment? Has it affected the overall look of the painting? Has the work been aesthetically compromised by past treatments?
Aided Examination
Once a conservator has done a visual evaluation, the next step is to utilize aided examination. Using techniques beyond visible light, the assessments made with natural light can be confirmed and elements of a painting’s struc-ture can be specifically identified.
Ultraviolet Light
Ultraviolet, or “black,” light is a light of short wavelength that causes materi-als on the surface of a painting to fluoresce. Aged, resinous varnish fluoresces green-yellow. Interruptions in the fluorescence of a resinous coating are usu-ally areas where the varnish has been removed. Retouches are normally visi-
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ble as lavender or purple areas. By comparative study of the retouches on a work, conservators can separate old and new retouching campaigns. Newer retouches appear as a darker purple (almost black), while old retouches are more lavender in color.A painting varnished or cleaned in the frame will show a different pattern of fluorescence around the perimeter where the frame rab-bet interfered with the application or removal of the varnish. A dark purple signature over a sea of green-yellow fluorescence should prompt the examiner to check whether the signature has been added, strengthened,or overpainted.
The information obtained from ultraviolet examination is surface infor-mation only, answering questions about what has happened on the surface of the painting. As with other investigative techniques, interpretation of ul-traviolet results requires experience.A painting with no greenish yellow flu-orescence could have no varnish, a new resinous varnish, a synthetic varnish, or a very old, very thin resinous varnish. The lack of purple retouches could indicate a painting in good state,old retouches well covered by a veil of heavy resinous varnish, an unusual retouching medium, complete overpainting, or a masking varnish.11 These masking varnishes have ultraviolet-filtering ma-terial added that retards the aging of the varnish and gives the painting mod-erate protection from ultraviolet light damage. For this reason, it also inter-feres with ultraviolet examination.
Infrared Examination
Infrared is at the long wavelength end of the spectrum.Because it is most sen-sitive to carbon-containing materials such as those found in the black pig-ments,black-and-white infrared studies often reveal underdrawings done with carbon inks or paints on light grounds.These underdrawings are best seen be-neath reds and crimsons,which are transparent to infrared.Underdrawing done in other methods—for example, chalk drawings on dark grounds—will not be visible with infrared examination.
Infrared images can be obtained with properly sensitive photographic film (infrared photography) or with a vidicon system (infrared reflectography). In-terpretation of these images, however, is not merely a matter of science. It must be done with historical knowledge about an artist’s workshop practice. An underdrawing that depicts developing ideas is more likely to be by the artist. A drawing using the squared grid, called a cartoon, represents a differ-ent,more mechanical method of production that could have been carried out by an artist’s workshop following the master’s design.
Color infrared photography has also been found to be useful in assessing artists’ materials. Color infrared film is a “false color film.” Two colors that appear similar in normal light can appear to be very different with color in-
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frared photography. In studies to determine the pigments in the blue areas of fourteenth-century Sienese panel paintings, the blue pigments azurite and ultramarine were easily distinguished when recorded with color infrared photography.12
In recent years, the publication of infrared studies has been increasing.13 As more reference material is available, authentication research using infrared im-ages will become more precise.
Radiography
X-ray images can expose the way a painting is created and are useful in re-vealing damage. Painting materials vary in transparency to X rays, with lead-containing pigments being the most absorptive. Ground layers that contain lead will reveal the weave and texture of an original canvas whose reverse is covered by a lining. Lead in the underpainting will expose the application of otherwise invisible layers of paint.Repairs, fills, and repaintings may absorb radiation differently than original paint and can become visible in an X-ray study. X rays are particularly useful in making comparisons.Within an artist’s oeuvre, they can show striking similarities in paint handling or in the fre-quency of pentimenti. However, there are always exceptions. In midcareer, Velázquez switched from lead white to calcite white in his paint layers.14
Without lead white, little or no design is visible in the radiograph. Compar-ing the resulting dissimilar X rays of works from Velázquez’s midcareer and his early works would wrongly lead the examiner to question the attribu-tion of some of his most important paintings.
Magnified Viewing
Magnified viewing begins with a jeweler’s loupe.Conservators usually choose loupes that magnify the surface of the painting five to ten times.With a loupe it is easier to differentiate texture and transparency of paint, to identify re-touches, and to examine cracks. Condition problems are also more evident.
Microscopic examination lets the conservator examine the cracks, the tex-ture, and the application of the paint even more closely.Magnifications of 25x to 50x are generally the most useful.Microscopic examination can reveal sig-natures and inscriptions to be original to the piece, clearly worked wet on wet into the paint, or to have been added at a later time, extending over cracks or old damages. It should be kept in mind that some signatures were legitimately added long after the work was completed: the artist may have kept the work and signed it only years later; and often an artist’s estate adds signatures to all the works held in its name. For this reason, some paintings
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from Corot’s estate appear to be signed twice—one signature inscribed by the artist at the time of painting and one added as an estate stamp.
Microscopic examination also extends to extracting and investigating cross sections of the layers of paint,which reveal the artist’s working method—the sequence in which paint was applied. Cross sections are usually viewed at magnifications of 150x–250x. Special staining and lighting techniques un-der the microscope can enhance various layers, making identification easier. For example, microscopic staining techniques were used in an investigation of works by Albert Pinkham Ryder (1847–1917). The forgery of his works began in his lifetime, thereby complicating the detection of counterfeits.Re-searchers used ultraviolet light microscopy and direct reactive fluorescent dyes to examine and compare the binding media used in three autograph works and five known forgeries. In the authentic paintings, the staining revealed a complex layering. In the forgeries, the results were very different. The mate-rials used were much more traditional, the layers were thicker, and the intri-cate intermixing which arose from the artist’s obsessive reworking was clearly lacking.15
While cross sections can be very revealing, without careful interpretation and investigation they can also obscure understanding of the painting. If, for example, varnish is found between paint layers,what does it mean? Is only the work beneath the varnish the work of the original artist? Is this an artist who added a varnish between paint layers to isolate or saturate them? Could the artist have revisited the work immediately or in later years? Is the small sam-ple being studied from an area where a varnish may have seeped between in-termediate layers of paint where there was a lacuna? Is the sample from an original area at all? Could it be a resin from a later conservation treatment? Often the information conservators get from microscopic study only raises more questions.
Microchemical Testing and Polarized Light Microscopy
Microchemical testing is done using a stage microscope. The operator views a tiny sample of the paint layer as it is brought into contact with a reagent. A reaction, such as a color change or effervescence,will indicate the presence of a specific pigment.The accuracy of microchemical testing depends on the freshness of the chemicals and the careful sampling technique of original paint. Inadvertent sampling from a retouch area, for example, would yield confusing results.
Polarized light microscopy uses focused light to illuminate the sample. Manipulating the sample and the light, an experienced investigator learns to identify materials. Good results from polarized light microscopy depend on
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accurate samples and on a microscopist who is familiar with the behavior of pigments and media under polarized light.Walter McCrone used polarized light microscopy to analyze the white pigments in Ballet Espagnol and Infanta Margarita, two paintings attributed to Édouard Manet. In three other works firmly attributed to Manet,he had noted the unique presence of an elongated lead white carbonate component.Comparing this white pigment against that in Ballet Espagnol and Infanta Margarita, he concluded that the two pigments “could not have been more similar if they had been squeezed from the same tube of paint.”16 McCrone’s technical analysis of the pigments confirmed the attribution to Manet.
Scanning and Transmission Electron Microscopy
Scanning electron microscopy enables the conservator to view samples un-der 1,000x to 10,000x magnification. A scanning electron microscope can also be used to identify elements within the pigments, thereby enabling the conservator to identify the pigments themselves. Because of the very minute samples that are magnified, it is crucial to ensure that the sample taken is rep-resentative of the artist’s work.
More recently, scientists have found that transmission electron microscopy is even more useful for characterizing inorganic compounds found in the paint and ground layers of paintings. This scientific tool can give more pre-cise analytical information at the same magnifications as scanning electron microscopy.
Autoradiography
Autoradiography is quite different from radiography. Undertaking autoradi-ography requires transporting a painting to a nuclear physics laboratory and housing it there for several months. The painting is exposed to low levels of radiation.A succession of images is then taken that records the rates at which the materials in the work emit the radiation. The images can be very in-formative, showing underdrawings that cannot be seen with infrared, reveal-ing the manner of paint application, distinguishing pigments, and recover-ing details of paintwork which have become obscure in dark areas. The interpretation of the multiple films obtained through autoradiography is, however, very complex.Accurate conclusions can be drawn only by consid-ering the results in conjunction with much comparative material, supported by information about the artist and his techniques.
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Other Scientific Techniques
Conservation scientists continue to work with other types of analytical equip-ment to identify and date supports, media, and pigments—and continue to inject a cautionary note.The refinement of radiocarbon dating,which looks at the organic materials used during the creative process, is one example.The accelerator mass spectrometer has made it possible to get results using very small samples.17 Interpreting the results, however, requires acknowledging the limitations of the technique. Radiocarbon dating determines the date that organic material was removed from the live carbon cycle. Finding the date a tree may have been cut down does not mean it was used immediately as a painting support.Wood could have been used for a piece of furniture or a door centuries before it was recycled as a panel support for a painting.An-other limitation is the margin of error inherent in mass spectroscopy, which may be too wide to allow researchers to distinguish works that are close in date.
Conclusion
Conservators, curators, art historians, collectors, auction houses, and dealers all search for the nugget of information that will attribute a painting to the hand of the artist with certainty. Nevertheless, although volumes of infor-mation about a painting’s materials and techniques may be yielded by a va-riety of analyses, from visible light to exotic tests, the certainty of attribution remains elusive. Often the only conclusion that can be drawn from the evi-dence is that there is no reason the work could not be by the hand of the artist.This careful double negative best expresses the limits of our testing and knowledge, and the frustrating reality that we cannot time travel to a distant century to see the artist creating the work.