Between a third to a half of all art works for sale in Czechia could be fakes, according to the Art Report 2023. The report, which surveys the main actors in the Czech art world, including collectors, dealers, and experts, found that forgeries are considered to be the biggest problem currently facing the domestic market and that the number of forgeries, especially of works of modern art, has been on the increase. But how are forgeries uncovered, and how can you test the authenticity of a painting?
Verifying the authenticity of a painting is no easy task, but fortunately, nowadays we have a number of methods at our disposal, says Vítězslav Knotek from the University of Chemistry and Technology. In addition to the expertise of art historians and appraisers, there are also chemical methods.
“We can find out the composition of the pigment used in the painting. Some modern pigments did not exist in the 18th century, for example. And on the basis of that analysis, we can prove that the artist couldn’t have used pigments that were created after his death.”
However, chemical analyses are not preferred in the case of an irreplaceable work, as the analysis requires microscopic samples to be taken from the painting, which damages it and decreases its value. In these cases, X-rays can be used instead to penetrate under the painting and see if it has been painted over, without causing any damage to it.
However, forgers could potentially make a copy of a painting on old canvas using historically accurate pigments. Chemical analysis alone would be useless in determining the authenticity of such a painting. This is where historical art expertise comes into play.
Not every repainted painting is a forgery, though, points out art historian Štěpán Vácha. He gives the example of a painting of Habsburg Emperor Rudolf II. In this instance, the work was not a forgery, but the hidden layers underneath helped to confirm that it had been painted by Hans von Aachen, one of the emperor's favourite court artists.
“For some reason – we don’t know why – the painting wasn’t finished or it was damaged. The artist had it in his studio and simply painted over it. That happened quite a lot. On the other side of the canvas, there is another unfinished painting by the same artist.”
When verifying the authenticity of paintings, experts have to rely on knowledge of the artist's individual working style, of how he tended to paint and whether he was prone to reworking his pictures. Sometimes if a painting is too perfect, it could be an indicator that it is a copy – but not always, says restorer Adam Pokorný from the National Gallery and the Academy of Fine Arts.
“There are also artists that stuck exactly to the original composition that they outlined at the beginning underneath their paintings, and never made any changes.”
The biggest challenge when investigating the authenticity of paintings is determining who exactly painted them. With some old works, even experts cannot reliably tell whether it is an original painting by the artist or a copy by a student or follower, says Štěpán Vácha.
“For example Lucas Cranach had a large studio with many students, so it’s hard to tell exactly what he painted himself. Or the famous painting Salvator Mundi – to this day, there are disputes over whether it’s an original by Leonardo da Vinci. You can find a whole bunch of cases like this in old art.”
New methods for determining the authenticity of artworks are still being developed – including using AI – and experts say they may help solve some of these famous old art mysteries.