On July 12 and 19 of this year (2025) I published a two part look at color perception among ancient peoples titled Could the Cave Artists Actually See Their Colors – parts 1 and 2. These explored theories that ancient people perceived fewer colors than we do today. While I do not agree with any of those positions I did have fun exploring the topic. Now I have found a paper that helps cast light on that question and may help provide an answer.
The discovery was made in Dzudzuana Cave, in Georgia, in the Caucasus. “In the foothills of the Caucasus, archaeologists have recovered something unusual from Dzudzuana Cave: tiny traces of indigotin, the molecule that produces indigo blue. The residues clung to pebbles used as grinding tools 34,000 years ago. They came not from food, but from the leaves of Isatis tinctoria L. – a plant better known as woad.” (anthropology.net 2025)
The evidence was found in grinding stones. “The leaf epidermis fragments were found entrapped in the topography of the used surface of unmodified pebbles, in association with use-wear traces. Although their bitter taste renders them essentially inedible, the leaves have well-recognised medicinal properties and contain indigotin precursors, the chromophore responsible for the blue colour of woad, a plant-based dye that is insoluble in water.” (Longo et al. 2025:1) Indeed, it is woad that is traditionally used in dying the denim for blue jeans.
“This is the first evidence that Upper Paleolithic groups intentionally processed a non-nutritional plant to extract compounds for purposes beyond survival. For archaeologists, it is a rare window into how Homo sapiens looked to plants not just for calories, but for color, healing, and meaning.” (anthropology.net 2025) So now the question is whether the I. tinctoria was ground for medicinal uses, or to obtain the blue colorant, or both.
“The ingestion of non-nutritional plants containing medicinal
secondary metabolites was identified in 47,000-year-old Neanderthal dental
calculus, while tentative evidence for poison 40,000 years ago was recovered
from Border Cave, South Africa. Medicinal plants are reported from a number of
Palaeolithic sites in the Caucasus; however, it is challenging to demonstrate
that these were ingested and/or intentionally processed. To date, there is no
evidence for the extraction of dyes from organic materials in the Palaeolithic;
the known colourants (red, yellow, black and white) are all pigments of mineral
origin apart from charcoal. They are highly resistant to ageing, with little
apparent degradation and known to have been used in Palaeolithic art and for
other purposes. For example, ochre is known in various applications such as
tanning leather or skin, as a preservative, as insect deterrent and as skin
protection.” (Longo
et al. 2025:2-3)
Also “this is the first time indigotin — a blue secondary
compound, also known as indigo — has been identified on such ancient artifacts.
The molecule forms through a reaction between atmospheric oxygen and the
natural glycoside precursors in Isatis tinctoria L. leaves, released from the
cellular vacuoles. This proves that the plant, despite not being edible, was
intentionally processed as early as 34,000 years ago.” (Ca’
Foscari University of Venice (Press
Release), 2025)
“Although a significant number of plants naturally contain useful secondary metabolites, many require complex processing to access these and make them usable. Even in the case of food, some nutritious plants require extensive leaching, roasting and/or pounding to eliminate toxins, while extraction of useful medicinal secondary compounds demands a deep knowledge of plants since many can be both medicinal and poisonous, with only the correct processing and dosage making the difference. The processing of plants cannot be simply assumed or ignored as it formed part of the complex tapestry of Paleolithic life. Nonetheless, to demonstrate the use of plants, exhaustive analytical studies are required and studies such as those presented here, is one way to achieve this.” (Longo et al. 2025:15-16) I think common sense allows us to infer a considerable range and variety of plant use during the Paleolithic.
“Many plants have extensive medicinal properties including anti-inflammatory, anti-tumor, antimicrobial, antiviral, analgesic, and antioxidant and there is extensive evidence for the use of these, not only in human traditional medicine, but also across the animal kingdom. All animals, and even insects, self-medicate. In the case of chimpanzees, they sometimes prepare the plants prior to consumption; Sumatran orangutans are known to apply to wounds a mashed concoction of Fibraurea tinctoria leaves. Today, the roots of I. tinctoria and other indigo-bearing plants are used in medicine because they contain flavonoids and the leaves contain indigoid-precursor molecules that have preservative, antiseptic, repellent, and protective properties. It is therefore entirely within the behavioral context of humans, from all Paleolithic periods, to use plants to self-medicate.” (Longo et al. 2025:17)
“I. tinctoria is also known as a source of indigotin, a well-established blue chromophore obtained by the oxidation of precursors naturally present in the cells of the leaves. The use of I. tinctoria to obtain a blue hue is well known, and this knowledge extends into later prehistory. The use of this plant has been recorded as dye since Egyptian times, the earliest written source being the Papyrus Graecus Holmensis (also known as the Stockholm papyrus, retrieved in the XIX century). However, while the possibility exists that I. tinctoria was transformed into woad dye and used during the Early Upper Palaeolithic, there is currently no archaeological evidence for this. However, and more broadly, color was known, in particular in rock art where red, yellow, white and black are present across the Eurasian continent and the Indonesian archipelago from around 40,000 years ago. Blue is a relatively rare color in nature and to the best of our knowledge, blue pigment (mineral-based) from Palaeolithic contexts has only been reported for Siberian figurines.” (Longo et al. 2025:17-18) Organic based paints (i.e. plant-derived) tend to disappear through oxidation and weathering over the millennia. I. tinctoria may have been used as a colorant for rock art but we may never know it.
Given that no known evidence remains of the use of I. tinctoria as a colorant from this long ago so it may well be that the intended use was medicinal, however, the fact that the people there were engaged in grinding it in preparation for something would seem to be proof that they could see it. So, the question of whether ancient painters could see blue or not 34,000 years ago is closed – as I said before, they could.
NOTE: Some images in this posting were retrieved from the internet with a search for public domain photographs. If any of these images are not intended to be public domain, I apologize, and will happily provide the picture credits if the owner will contact me with them. For further information on these reports you should read the originals at the sites listed below.
REFERENCES:
Anthropology.net, 2025, The Blue Shadows of Dzudzuana, 2 September 2025, https://anthropology.net. Accessed online 3 September 2025.
Ca' Foscari University of Venice (Press Release), 2025, Traces of blue indigo on 34,000 year old grinding tools suggest Paleolithic plant use scenarios, https://phys.org/news. Accessed online 2 September 2025/
Longo, Laura et al., 2025, Direct evidence for processing Isatis tinctoria L., a
non-nutritional plant, 32–34,000 years ago, 9
May 2025, PLOS One, https://doi.org/10.1371/journal/pone.0321262. Accessed 3 September 2025.
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