A painting can reveal far more than what is visible on its surface. Earlier compositions may lie concealed beneath the paint, a wooden panel may contain information about the age of the timber from which it was made, and pigments can provide indications of the earliest possible period in which a work could have been produced.
Even old restorations, overpainting and alterations made by the artist during the painting process can now be made visible. This does not mean, however, that a laboratory test can simply determine who painted a particular work. Authentication rarely works in such a straightforward manner.
A convincing attribution is established by considering different forms of evidence together: art-historical research, provenance research, the examination of style and painting technique and, where appropriate, scientific analysis of the materials. It is precisely the combination of these approaches that matters.
A pigment that did not become available until the nineteenth century, for example, may pose a serious problem for a painting purported to date from the seventeenth century. The reverse, however, is not true: finding only materials that were available in the seventeenth century does not automatically prove that Rembrandt, Van Dyck or another Old Master painted the work.
Examination Does Not Begin in a Laboratory
It is generally not sensible to begin immediately with X-radiography or pigment analysis. The first stage of examination is considerably simpler. One looks. And not merely at the subject of the painting, but at the object as a whole. The front and back, the support, stretcher or panel, frame, labels, seals, old inventory numbers, inscriptions, damage and restorations can all contain valuable information.
This may seem self-evident, yet this stage is often underestimated when privately owned paintings are examined. A dealer’s label may provide information about provenance. An old auction number may lead to a historical catalogue. The construction of a panel may correspond to a particular regional tradition. An unusual format may indicate that the painting was reduced in size at some point. A signature may lie on top of an older craquelure pattern, suggesting that it was added later.
Microscopic Examination: Looking Closely at the Paint Surface
Magnification reveals details that are easily overlooked by the naked eye. Among other things, it allows the examiner to study the structure of individual brushstrokes, craquelure, pigment particles, damage, retouching, varnish layers and the relationship between a signature and the surrounding paint.
An old paint surface may contain several historical layers lying one above another. An area that appears entirely homogeneous to its owner may, under magnification, prove to consist of original paint, an aged varnish layer and subsequent retouching.
A conservator who repaired an area of damage in 1950 may, after all, have introduced modern paint onto a seventeenth-century painting. If a modern pigment is subsequently detected without considering its location and context, one cannot conclude that the entire painting is modern. The location of an observation is therefore at least as important as the observation itself.
Raking Light: Revealing the Surface Relief of a Painting
One particularly simple but useful technique is examination under raking light. The light source is positioned at a very shallow angle, almost parallel to the surface of the painting. Even minor variations in height consequently cast relatively pronounced shadows.
Impasto — paint applied thickly and with a pronounced body — becomes considerably easier to see. Distortions in the canvas, old damage, seams, localised restorations and irregularities in the underlying support can likewise become more apparent. Raking light provides no chemical information and does not directly tell us how old a painting is. It can, however, help us understand how the object is physically constructed and identify areas in which further investigation may be worthwhile.
Ultraviolet Fluorescence: Examining Restorations and Varnishes
When a painting is examined under ultraviolet light, certain materials may fluoresce. The resulting appearance can differ considerably from what is visible under normal illumination. UV examination is particularly useful in the study of varnish layers and restorations.
Older natural varnishes can exhibit characteristic fluorescence under ultraviolet light, whereas some later retouchings appear as dark or otherwise anomalous areas. The resulting image can therefore function as a kind of map of the painting’s restoration history. There is, however, an important limitation: a UV image is not an automatic test of age.
Fluorescence is affected by the type of material, its age, the thickness of the layer, previous treatments and various other factors. Interpretation requires experience and should be combined with examination under visible light and, where necessary, additional material analysis. For an owner, such an image can nevertheless be particularly revealing. A painting that appears almost completely untouched at first sight may show extensive restoration when viewed under ultraviolet illumination.
That is not necessarily a negative finding. Many important paintings have undergone restoration during their lifetime. The essential question is to distinguish what is original, what was added later and what condition the original paint surface is in.
Infrared Reflectography: Looking Beneath the Visible Paint
One of the best-known techniques in the technical examination of paintings is infrared reflectography, usually abbreviated to IRR. Certain paint layers that are opaque to visible light can be comparatively transparent to infrared radiation. Carbon-containing materials beneath the paint, by contrast, may absorb infrared radiation strongly. Under suitable circumstances, this makes it possible to reveal an underdrawing.
The results can sometimes be spectacular. Beneath the painted composition, lines may emerge that were used by the artist in preparing the design. Alterations to hands, faces, clothing or architectural elements may become visible. In some cases, a figure proves originally to have occupied a different position.
Such changes are often referred to as pentimenti. For questions of authorship, this type of evidence can be particularly interesting. Not because every artist invariably employed one specific form of underdrawing, but because preparatory methods can form part of a broader technical pattern within an artist’s oeuvre or workshop.
X-Radiography: The Internal Structure of the Painting
X-radiography operates according to a different principle from infrared reflectography and consequently provides different types of information. Materials absorb X-rays to varying degrees. Pigments containing elements with relatively high atomic numbers, for example, can appear particularly clearly in a radiograph.
This can provide information about the distribution of particular paint layers, but also about the construction of a panel or other structural components of the object. X-radiographs can reveal earlier compositions, show alterations made during the painting process and provide information about the physical construction of a work.
One of the best-known advantages of X-radiography is that a painting may sometimes quite literally contain another painting beneath it. Artists reused supports. Compositions were altered. Figures disappeared beneath later paint. A portrait may originally have shown the sitter in a different pose.
An interesting X-radiograph does not, however, make a painting authentic. A follower, workshop assistant or forger may also have made changes during the painting process. The evidence acquires meaning only when the technical image is compared with documented works and with historical painting practices.
XRF: Examining the Elements Present in Pigments
X-ray fluorescence spectroscopy, commonly abbreviated to XRF, can be used to investigate which chemical elements are present in or near the surface of a paint layer. This is not the same as identifying a pigment directly. If lead is detected, for example, this may be associated with a lead-containing pigment. Precise interpretation nevertheless requires consideration of the location of the measurement, the stratigraphy of the paint and the presence of other elements.
XRF results are therefore frequently combined with other analytical techniques. An important advantage of XRF is that in many applications it can be performed non-destructively. In scanning macro-XRF, a large portion of the painting is systematically analysed, allowing distribution maps of particular elements to be produced.
This can reveal concealed forms and compositional alterations while also providing information about the materials employed. For questions of dating, such analyses can be significant when materials are detected that are historically incompatible with the proposed period of execution. Yet it is essential to establish where those materials occur: they may, for instance, be confined entirely to a later restoration.
Raman, FTIR and Other Spectroscopic Techniques
When it is necessary to determine more precisely which chemical compound a particular material consists of, other analytical techniques become relevant. Raman spectroscopy and Fourier-transform infrared spectroscopy, or FTIR, can assist in the characterisation or identification of pigments, fillers, binding media, varnishes and other organic or inorganic substances.
For a private owner, the precise physical principles behind these methods are usually less important than the research questions they can answer. Is the blue pigment compatible with the proposed date of the painting? What is a particular varnish composed of? Is a material original, or does it most likely belong to a later restoration?
Serious material analysis should therefore begin with the question: “Which hypothesis are we trying to test?” This prevents costly examinations from being carried out that ultimately reveal very little of significance about the painting.
Paint Samples and Microscopic Cross-Sections
Some questions cannot be answered through imaging techniques alone. In specialised cases, an extremely small sample of paint may be removed. The sample can be embedded in resin, polished and examined microscopically as a cross-section.
This reveals the stratigraphy of the painting: the sequence of ground layers, underpainting, individual paint layers, varnishes and, potentially, later restorations. Because material must actually be removed from the painting to produce a cross-section, this is an invasive technique, unlike many imaging methods. Sampling should therefore be carefully targeted and kept to an absolute minimum.
Dendrochronology: The Tree Rings of a Wooden Panel
Paintings executed on wooden panels offer another particularly interesting possibility: dendrochronological examination. Trees produce annual growth rings, the width of which varies from year to year in response to climatic conditions. By comparing sequences of growth rings with dated reference chronologies, the timber used for certain panels can be dated.
Dendrochronology is therefore regularly used in the examination of historical panel paintings. Yet dendrochronology, too, is often misunderstood. The method primarily dates the wood, rather than directly establishing the year in which an artist completed the painting.
A period of time may have elapsed between the formation of the last measurable growth ring, the felling of the tree, the processing and seasoning of the timber and the actual painting of the panel. In addition, the outermost rings may be missing because they were removed when the plank was cut and prepared. Dendrochronological analysis therefore generally provides a terminus or a range of possible dates rather than a simple statement such as: “this painting was made in 1632”.
Examination of Canvas and Other Supports
Not every painting was executed on a wooden panel. In paintings on canvas, the weave, thread count, seams, method of stretching and the edges of the canvas can all provide important information. Advanced analysis of canvas structures can even help establish relationships between paintings that appear to have been cut from the same roll of fabric.
The edges of a painting are therefore important as well. Has the original format been preserved? Are old tack or nail holes present? Has the canvas subsequently been lined with a second canvas? Was the painting cut down at some point? Is the stretcher compatible with the proposed period? Such apparently modest details may ultimately prove more significant in an attribution study than a spectacular laboratory image.
Can Technical Examination Prove Who Painted a Work?
This is ultimately the question that interests most owners. The short answer is: rarely on its own. Technical examination is particularly powerful when it comes to excluding possibilities.
If a painting attributed to an artist who died in 1720 can be shown to contain a material that only became available much later, and if that material can be demonstrated to belong to the original paint layer, the attribution faces a fundamental problem.
Technical investigation can also reveal positive correspondences. The same type of panel construction. A comparable ground layer. A characteristic underdrawing. A similar build-up of paint layers. Materials corresponding to those found in other documented works. But correspondence is not the same as identification. A workshop assistant may have used the same materials as the master. A contemporary may have been familiar with the artist’s technique. A skilled follower may have worked with historically appropriate materials.
Authentication of important paintings is therefore generally interdisciplinary. Museum research projects combine X-radiography, infrared reflectography, dendrochronology, microscopy and material analysis precisely because painting technique and the history of an object’s manufacture must be understood as a whole.
Not Every Painting Requires Laboratory Analysis
When someone owns a painting whose artist is unknown, it is easy to assume that expensive technical analysis should be the first step. Usually, it should not. A logical investigation begins broadly and becomes progressively more specific. The first task is to establish what is actually in front of us: the subject matter and likely period, the type of support, any visible restorations and, above all, which art-historical hypothesis is plausible in the first place.
Only then does the question arise whether additional technical examination is likely to provide useful new information. If, stylistically, a painting clearly dates from around 1900, for example, there is little point in undertaking dendrochronological research in an attempt to establish a supposed seventeenth-century origin. Following the correct sequence does more than save money. It also prevents technical data from being collected without a clear understanding of what those data might actually mean.
Do You Own a Painting You Would Like to Know More About?
An unexpected discovery rarely begins in a laboratory. More often, it begins with a painting that has hung in a family home for many years, an illegible signature, an old label on the reverse, or simply the impression that a work may be better than the name under which it was once sold.
Not every unidentified painting turns out to be important. But some works deserve further investigation. Anyone wishing to determine whether further research would be worthwhile does not need to have the painting scientifically analysed immediately. Good photographs can often already provide enough information for an initial assessment.
Do you have a particular interest in this artist or in this subject?
Do you follow this artist, or have you come across a work you would like to know more about? We regularly research works appearing on the market and are always happy to exchange views on quality, provenance, art-historical context and previous auction results. You can contact us directly via info@antonello.art.