New Discoveries about Paleolithic Culture through the Analysis of Indigotin
10.10.2025
An international research team, coordinated by Ca’ Foscari University of Venice in collaboration with the University of Padua, has discovered traces of indigotin on stone pebbles dating back to the Upper Paleolithic. Indigotin is a blue dye derived from the leaves of Isatis tinctoria L., commonly known as woad, a biennial plant belonging to the Brassicaceae family and native to the Caucasus. This discovery, published in the scientific journal PLOS One, represents the first identification of a plant-derived organic dye molecule on artifacts this ancient.
The presence of indigotin shows that the plant was intentionally processed through a complex method, despite being inedible. This suggests that Upper Paleolithic populations used plants not only as a food source, but also for more complex functions such as dyeing and medicinal use.
“Our multi-analytical approach opens new perspectives for understanding the technological and cultural complexity of Upper Paleolithic populations, who were able to skillfully exploit an inexhaustible resource—plants—being fully aware of their potential,” explains Laura Longo, archaeologist at Ca’ Foscari University of Venice and lead author of the study.
“The research initially aimed to understand the function of stone tools, when unexpectedly it revealed the presence of blue residues, sometimes fibrous and associated with starch granules, concentrated in areas of the tools showing wear marks,” says Mauro Veronese, PhD candidate at the University of Padua and co-author of the study. Spectroscopic analyses at the NOL laboratory of the University of Padua subsequently identified and chemically characterized these blue residues, leading to the discovery.
Once the molecule responsible for the blue color was identified, a new challenge emerged: understanding how and why these residues ended up on those tools. Subsequent experimental archaeology involved collecting lithic raw materials and mechanically processing plants, including Isatis tinctoria, to replicate Paleolithic conditions and identify use-wear traces and plant residues.
Over the course of three summers, at Corte Badin in Marano di Valpolicella, Verona, experiments were conducted during which Isatis tinctoria plants, cultivated by farmer Giorgio Bonazzi, were ground using selected pebbles. The resulting materials enabled the creation of a reference collection to recognize use-wear traces and plant residues.
This interdisciplinary and innovative approach has shed light on the early use of plant-based compounds in the Paleolithic, highlighting the sophisticated use of available plant resources and opening new perspectives on the technological and cultural complexity of Paleolithic populations and the behavior of prehistoric humans.
