The imitation of works of art, from paintings to sculpture, has been carried out for hundreds of years. Students and followers have always made copies of the works of master artists as part of their instruction. There are many artists, both amateur and professional, who like to paint or draw in the style of those they admire. There is nothing morally wrong or illegal with this kind of copying or imitation. Art forgery, however, is different. It involves passing a copy of the artist's work off as created by the original artist, usually for financial gain. Where fraud or deception is involved, establishing whether a work of art is a forgery becomes a forensic investigation.
Art forgery can be extremely difficult to detect and investigate. There may be many forged works of art in museums and galleries around the world, and in private collections. Experts may be unaware if the forgery is accomplished cleverly, of the existence of a forged artwork, or they may be reluctant to admit they have been deceived. Sometimes the forger is more interested in getting the better of a dealer or collector than they are in their own financial gain. In such cases, transactions may be covered up and it is difficult to prove whether a criminal act has actually taken place.
For instance, the Spanish surrealist painter Salvador Dali (1904–1989) gave away around 20,000 blank sheets of paper with his signature, triggering a flood of forged Dali prints. Dealers would pay $2,000 to $20,000 for these fake prints. The art world also abounds with fake Picasso, Chagall, and Miró prints—to the extent that some experts are now reluctant to authenticate prints from certain modern artists because of the sheer volume of work it involves.
Distinguishing an authentic work of art from a forgery requires a blend of technical expertise and a profound knowledge of art history and the work of individual artists. Forgers do, however, often give themselves away even before laboratory analysis of their work begins. They often add an element of their own natural style, or they may unknowingly include some contemporary period detail that the historian will notice immediately. Art experts also comment on a "lack of freedom" to many forgeries, as the forger sometimes uses more rigid brush strokes or lines to capture details of the original work. After all, the thought processes of a grand master creating a work of art is quite different from those of someone far less talented who is merely trying to imitate him or her. Often this difference will spill out into the work, although the forger may not be aware of it.
A full analysis of a possible forgery, however, must rely on more than the expert opinion of an art historian. A laboratory analysis of the materials used to create the work is required, using techniques such as X-radiography and infrared reflectography. Modern artistic materials, such as paper, inks, and paints are different in composition today from those used hundreds of years ago. It is true that old materials can be re-created and used today, so one could, theoretically, fake a Rembrandt in the twenty-first century using seventeenth century style materials. However, the presence of acrylic paints, which first became available in the 1930s, would readily give away a Rembrandt fake. Rembrandt remains one of the most imitated artists of all time. To complicate matters, his signature is often found on works done by lesser artists. Works of art also age from the moment they are created owing to exposure to the atmosphere, handling, and other factors. The expert forger may try to artificially age his or her work to make it look as if it was created long ago.
Although many types of artwork are forged, the examination of a typical oil painting illustrates many of the general principles of detecting a forgery. A painting is composed of four layers: support, ground layer, paint layer, and varnish. The support is often made of wood or canvas. The analysis of a wood support can be very informative because modern fakes are often painted on older wood panels to make them look authentic. Dendrochronology , the examination of growth ring patterns, can sometimes be used to age the wood itself. X rays will penetrate to the wood layer and reveal the construction of a panel, including features like saw marks. Manual saws were used to make artists' supports before the introduction of mechanical saws during the nineteenth century Industrial Revolution. Manual saws leave characteristic uneven marks. If the investigator finds regular saw marks on a painting claimed to be of seventeenth century origin, this will be a strong indication of a fake.
The investigator might focus on the edge of the painting, using a special magnifier or infrared light to detect the nature of the ground layer. Such testing is non-destructive to the painting. Sometimes an invasive test might be carried out. This is not quite a bad as it sounds; a tiny pinprick is made in the painting, perpendicular to its surface and the sample extracted. If the sample is taken at the edge of a painting, or at an area that is already damaged, the harm done to the work is minimal. This cross-sectional sample can then by studied by x-radiography or microscopy to reveal all four layers and their composition. These can be compared with cross sections of authenticated work from the artist to see if there is a resemblance.
A technical examination of the paint layer can help to confirm a work's age and authenticity. The investigator will look at the materials themselves and how they were handled, which may be characteristic of the individual artist. The pigments that give paints their color have evolved over time and this history is quite well known. Earth colors, derived from minerals such as iron oxide came first, followed by greens (malachite), blues (azurite), and black (charred animal bone). Animal and vegetable dyes such as indigo and saffron also have a long history. The nineteenth century saw the introduction of synthetic dyes such as the anilines. These were far more chemically and physically stable. Analysis by visible spectroscopy can reveal the chemical composition of an organic pigment and x-ray analysis might be used for inorganic pigments such as titanium dioxide. If the pigments prove too modern for its alleged date, then there are various possibilities. The work may be a forgery, a genuine painting which has been touched up, or the dating may be in error.
Examination and photography of the paint layer with a microscope or magnifying glass, perhaps using light directed at an angle, is important. Surface irregularities may be observed, as well as features such as tiny particles arising from the use of hand-mixed pigments. Ready-mixed pigments, which have a smoother appearance, are a more modern development. Examination of the paint layer in ultraviolet light can show re-painted areas as dark spots. A re-paint is not necessarily a sign of forgery; some artists re-painted as a matter of course. If a re-paint is found in the work said to be of an artist who did not alter their work, then it is cause for suspicion. This may be a sign of a forger trying to correct a mistake. Similarly, infrared reflectography can reveal underdrawings in a painting. The paint layer is transparent to infrared light that passes through, but is absorbed by drawing lines beneath and reflected by the rest of the ground layer. This creates an image of the underdrawings in infrared light that can be photographed. While some artists would begin their work with a sketch used as a basis for the painting, others never did. The investigator would be alerted if an underdrawing was revealed in work alleged to come from one of the latter. Conversely, the lack of an underdrawing might be indicative of forgery, if it was said to come from an artist who never did them.
The aging of paint shows itself by a characteristic cracking pattern known as craquelure. Examination of the surface of the paint with a magnifying glass will reveal whether the extent of the craquelure matches the alleged age of the painting. Many paintings are varnished to protect them and enhance their appearance. Like paint, different varnishes have evolved over time. Ultra-violet light can distinguish between varnishes. Synthetic varnish gives a clear or lavender fluorescence (emission of light), while shellac fluoresces orange. Varnish discolors with time and this can also help date a painting.
Besides examining the four layers of a painting, the investigator will also look out for other significant signs of authenticity. Some manufacturers of artists' material marked their products with a stamp and there are databases giving information, including dates, of these stamps. The presence of collectors' marks or other signs that a painting has been owned, sold, exhibited, or framed can help establish the history of a work of art. Some artists signed their work and the forger may attempt to forge their signature. Strange as it may sound, a forger may create a copied artwork, complete with the artist's signature, quite legitimately. It is only when they offer this work for sale at an inflated price and attempt to represent the work as an original, that they enter the realms of forgery. The law on selling, buying, and owning forged works of art varies from country to country. Therefore, the amount of criminal investigation that will be carried out into a particular work depends upon context and circumstances. However, the forging of a certificate of authenticity to accompany the work of art is always considered a criminal offense, and can also be investigated by a forensic document examiner.
see also Art identification; Document forgery; Paint analysis.