Distinction of original and forged lithographs by means of thermogravimetry and Raman spectroscopy

Thermal analysis has been used to study the composition of paper and paper-like materials for some decades. The application of these techniques permits to distinguish between the original paper which was used by the artists and possible forgeries. Quite often, however, the identification of the differences demands the simultaneous application of several other techniques. The present investigation includes Asiatic wood-prints from China and Japan, and lithographs of European artists, such as Pablo Picasso, Salvador Dali, and Marc Chagall. Utamaro (1753-1806) is one of the most celebrated artists in the history of the Japanese woodblock print. He became one of the famous painters of 'Ukiyo-e' (Ukiyo-e means transitory world). In China Utamaro's pictures were also produced. The differences are found in the kind of paper: The Japanese used Mitsumata paper, while the Chinese printed on Bamboo paper mixed with silk fibers. Hu-ju-zong (Nanking, 1619) and a group of famous Chinese painters created the book of the 'Ten Bamboo Studio' which contains woodblock prints as visual aids for young artists. A reprint of these woodblock prints appeared in 1717. Later, a bootleg of this book appeared in Japan (1817). The differentiation is possible by thermogravimetric investigation of the used papers. Statistic evaluations in Europe show that more than 1 000 000 bootleg copies of lithographs of Pablo Picasso, Salvador Dali, and Marc Chagall exist. Thermoanalytical measurements allow the distinction between the original artifacts and the bootlegs. Raman spectroscopy gives an additional possibility for the distinction between the applied color pigments.