36,000-year-old blue indigo discovered by Ca’ Foscari

A team led by the University of Venice opens new insights into the capabilities of Homo Sapiens

“It seems unbelievable to think that our research work ended up in the prestigious journal PLOS thinking that we made this discovery almost by accident,” says Professor Laura Longo, a research archaeologist at Ca’ Foscari University in Venice. ” The idea came from a grant for a project written together with Elena Badetti, professor of Chemistry of the Environment and Cultural Heritage at Ca’ Foscari disbursed by the U.S.-based The Leakey Foundation to study stones preserved at the National Museum of Georgia in Tbilisi. We were supposed to analyze traces of starches to demonstrate the use of these tools to grind roots into flours, but instead … We discovered traces of indigotin, a blue dye, which is obtained from the leaves of Isatis tinctoria L., known as ford, a plant native to the Caucasus. This means not only did prehistoric man know colors, but he also knew how to obtain indigo blue pigment.”

The original research project, written in 2021, was favorably evaluated by as many as six reviewers, and the grant provided access to the artifact sampling campaign in Georgia. “The initial goal,” the archaeologist explains. was to understand how Archaic Homo Sapiens differed from Neanderthals thanks to artifacts found at the Dzudzuana cave site on the slopes of the Caucasus Mountains in Georgia, formerly excavated in the 2000s by a team formed by Harvard University, the National Museum of Georgia and Hebrew University in Jerusalem. The tools found at the time belong to the Upper Paleolithic dated between about 34,000 and 36,000 years ago. In addition to analyses on the stones, we also considered sediment samples extracted directly from the cave floor ».

Professor Laura Longo in the Dzudzuana cave in Georgia on the Caucasus

Indigo: the ancient blue pigment discovered by Ca' Foscari researchers

“Finding this substance together with traces of starch really surprised us and conditioned the field development of the whole research,” Longo says. the groundbreaking significance of this discovery, evidenced by the fact that we have been taken up by scientific journals and the international press, is that it shows that our ancestors were more evolved than we thought until now, so we should also change the way we have tried to understand until now how homo sapiens represented themselves and what idea they had of themselves, because the extraction of indigotin testifies that he was able to deal with complex processes of processing that were the result of observation and experimentation, since it takes months from grinding the leaves to obtaining the pigment, this points to the fact that already at that time evolution had allowed not only to observe to also understand determinant phenomena, defining correlations between cause and effect ».

“If thinking that grinding a leaf can be a trivial operation,” the academic adds. it must be stressed that it is necessary to know the life cycle and evolution of this plant precursor of indigotin, which at that time grew only on the Caucasus in the area of Eurasia. This gives insight into how these archaic peoples were already endowed with “ingenuity,” that is, a great ability to produce complex thought to carry out elaborate actions. In addition, continuing this line of research will serve to shed light on the use of this pigment, hypothesized to be used to be able to dye textiles or tan skin, but also for curative purposes given its antioxidant properties. This could also provide answers about the tradition of the use of Isatis tinctoria L., tracing it back to an earlier use than that known during the Middle Ages, especially in Italy along the Via Francigena to Toulouse, which was dotted by number dyeing workshops, so much so that several towns were named precisely “gualdo” ».

Indigotin fibers studied under a microscope

The research work done on indigo traces by the team led by Ca' Foscari

“Finding these residues made everything much more fascinating but also complex,” the researcher confides. this required a lot of work and the activation of different synergies because from an initial understanding of the function of the artifacts, we moved on to analyzing the plant residues under the microscope to study the blue fibers found on the areas of greatest wear of the artifacts, a sign that they were not elements of contamination, but of actual processing. The team from the University of Venice, formed in addition to myself by my colleague Badetti, Clarissa Cagnato, Giusi Sorrentino, supported by Antonio Marcomini, collaborated with technicians to the instrumentation of the SYCURI research infrastructure, from the University of Padua, thanks to the identification of a candidate for an ad hoc PhD in the person of Mauro Veronese, under the supervision of Moreno Meneghetti, Alfonso Zoleo and Gilberto Artioli.”

“In fact, once we identified the blue-colored molecule, we wanted to know more about it ,” Longo says. looking forhypotheses as to why residues were found on those tools to confirm the use of plant resources by early sapiens. In good probability, since plants were a much more accessible resource than animals, our ancestors had a good knowledge of them, having understood that when exposed to the air these would oxidize and that they could have medicinal properties, as in the case of gualdo, which besides changing color was useful for stomach pains and wounds. So from its processing a mush was obtained which, when dried, formed a kind of ball that could be ground or dissolved as needed. Precisely for this reason, by analyzing the porosity of the stones, thanks to synchrotron light, we were able to replicate experiments using the same materials with pebbles collected by Nino Jakeli in the Nikrisi riverbed and Isatis tinctoria L. plants grown by Giorgio Bonazzi in Valpolicella ».

Professor Laura Longo with part of the research team

Implications of the discovery of indigotin use by Ca' Foscari researchers

“The discovery was really important because it is only the starting point,” the scholar adds. these stones proved to be rich in history and information, and the in-depth study of their residues was possible thanks to collaboration not only between different universities, but also between multidisciplinary knowledge and expertise, so much so that we were able to allow true replicative archaeology with experiments carried out with stones of the same porosity and specially cultivated plants, following their natural cycle, committing ourselves for a year just to respect the cycle of nature. Overall, this was a three-year effort that allowed us to see beyond what was hitherto reading about the activities of early sapiens, and this was possible thanks to the collaboration between chemists and STEM experts and humanists ».

“It was precisely this pooling of viewpoints, sensitivities and experiences that allowed for a situation of ‘serendipity‘ that enabled this important discovery,” Longo concludes. the most memorable thing is to know that our ancestors were already thinking in using a kind of “pantone“-there were not only the pigments that have come down to us like the red, black, and yellow observed in caves, but there was probably a richer color vocabulary. We are moving beyond the archaeology bias of relying only on what we can see, but together with technology, learning from each other by working together with scientists, it is possible to write many new chapters in human history. We are already characterizing various types of molecules and lignins ( organic polymer complexes) for different species of Isatis, because we would like to continue this line of indigo studies, funding permitting!“.