“Invisible stamp” developed by Czech scientists could help identify stolen documents
Czech scientists have developed a unique “invisible stamp” that could help identify the owners of rare documents or works of art that got lost or stolen. The stamp is not detectable to the human eye and can only be deciphered by an X-ray fluorescence spectrometer.
Historical documents in archives are usually marked with a classic metal or self-inking stamp with the name of the relevant institution. However, this simple and widespread method has its drawbacks. First of all, it is visible, which reduces the aesthetic value of the printed material. And second, commonly used stamp inks can be easily removed.
This is what prompted experts from the Faculty of Chemistry at the Brno University of Technology to work on developing a new identification element, explains the faculty’s dean Michal Veselý:
“In the past, when some archival documents were stolen, it was very difficult for the owner to prove ownership of these works, because the stamps were removed before they appeared at an auction.”
Together with other institutions, experts from the Brno University developed a unique stamp, based on rare metals, explains another member of the research team, Petr Dzik:
“Just as the bar code has lines and spaces of varying widths, our code contains exotic metals that are present in very small quantities in a regular environment. When we read the code with a special portable device, we are able to interpret it.”
The stamp can withstand time, heat, light, mechanical abrasion and restoration intervention. At the same time, it is completely invisible to the ordinary eye and cannot be detected even by the classical UV method.
The technology enables scientists to use as many code variations as possible, based on the number and proportion of metal oxides used in the printing mixture, explains Mr. Veselý:
“The finished mixture is pipetted into the printing machine and the printing varnish is transferred onto the archival material using a silicone pad. When it dries, it will no longer be visible. That's why we added a special powder that glows green when irradiated with an infrared laser, so we can find the mark.”
To mark a document or a work of art with the invisible stamp is a simple process. The interested party will receive a unique tailor-made varnish. It can then be added to any printer using the pad-printing technique. The stamp can be used not just on paper, but also on other materials, including glass, plastic or metal.
The special stamp developed by the scientists from Brno has already been patented and a number of private companies and state institutions have already expressed interest in the invention. However, in order for the technology to be put in practice, an institution must be established that will allocate the codes to interested parties and maintain their database.
