Policie České republiky – Kriminalistický ústav
2
Obrazy, šperky, drahé kameny, ...
PAINTINGS, JEWELLERY, PRECIOUS STONES, ...
Today's art market is flooded with fakes. It is estimated that at least one-third of paintings sold on the world market are fakes. Physical chemistry experts in the Institute of Criminalistics also, very frequently, examine counterfeit jewellery and precious stones. A 'bargain' purchase on the Internet or from unauthorised dealers may therefore not be worthwhile.
1. Fake paintings
Forgeries of the 20th century Czech masters are very common
In recent years, our experts have examined a large number of paintings that were thought to be fakes. The most frequent forgeries offered on the market are those of František Kupka, Jan Zrzavý, Kristian Kodet, Emil Filla, Václav Špála, Jan Kotík, etc. In many cases, these are sold with expert opinions of private experts who usually base their conclusions only on subjective assumptions. However, laboratory analyses are often necessary to verify the authenticity of the painting.
2. Taking a sample from a painting
Complex examination of a work of art
A painting is first subjected to a multispectral and X-ray imaging. Experts thus determine whether any overpainting etc. has been applied and the artist's 'handwriting' (style) can also be compared. The only destructive method of painting examination is an extraction of a miniature sample of paint (of the size smaller than a pinhead) from selected parts of the painting. The collected samples are examined under a microscope meaning that the structure of the whole paint layer can be mapped. Using an electron microscope, chemical composition of paint pigments is analysed. The experts examine if the paint used in the examined painting corresponds the chemical composition of the paint the painter used in their original work. There are also other methods applied, e.g. X-ray diffraction, Raman and infrared spectroscopy, etc. Forensic examination of paintings is complex. Attention is paid for example also to fibres, wood and frame construction or the painter´s signature.
3. X-ray backlight of overpainting
Fake jewellery
Experts commonly encounter jewellery declared to be gold, but which is in fact only gold-plated or covered with a thin layer of titanium nitride which imitates gold very well. The jewellery itself is made of common cheap metals.
4. Fake gold imitation
Diamond or cubic zirconia
Modern industry can produce high quality imitations of precious stones. One of them is the so-called cubic zirconia (zirconium oxide), which has physical properties close to diamond and even surpasses it in optical dispersion. It can be of any colour and can thus be used to imitate almost any gemstone. Another imitation of diamonds is the so-called moissanite (silicon carbide). Because of its excellent physical properties, it is increasingly being used to imitate diamonds. Our experts have also examined jewellery declared to contain Bohemian garnets. In reality, however, these were cheap garnets of a different origin and composition, which were offered by dealers as Czech garnets. These garnets often differ from the Czech garnets in colour. They are masse-sold, especially in places with a large concentration of tourists.
5. Electron microscope