Writing in Roman Antiquity was not only an intellectual practice: it was based on precise technical know-how and complex materials, often invisible in the traces left by the past. In Conimbriga, central Portugal, the discovery of a bronze inkwell from the 1st century CE revealed exceptionally well-preserved ink residue, allowing detailed analysis of its composition.
Led by an interdisciplinary team from the University of Évora, the University of Coimbra and the HERCULES laboratory, the study was published in Archaeological and Anthropological Sciences. She identified for the first time on the Iberian Peninsula a “mixed” ink composed of carbon black, bone black, iron gall elements and organic binders. This result requires us to review preconceived ideas about the diffusion of written technologies in the Roman Empire, particularly in its most remote provinces.
An elite inkwell in the heart of a provincial town
Discovered in Conimbriga, an ancient Roman city located in what is now central Portugal, the bronze inkwell unearthed in 2022 is of the Biebrich type. This model dates from the first half of the 1st century AD. This type of object, common in the military regions of Northern Italy and the Upper Rhine, had never been found in the Iberian Peninsula before this discovery. The object comes from a level of embankment linked to the demolition of the Roman amphitheater. Which suggests that it belonged to a person involved in a major project: architect, surveyor or administrative official.
© C. Oliveira et al., 2025
Map of Conimbriga showing the location of the discovery of the inkwell (A). Detailed view of the archaeological context of its discovery (B).
The inkwell, weighing 94.3 grams, is made from an alloy of copper (79%), tin (11.5%) and lead (8.9%). The significant presence of lead remains significant. Indeed, it improves the fluidity of the molten metal, allowing thin walls and high precision machining. Concentric turning marks visible on its surface indicate lathe shaping. A technique mastered in the specialized workshops of the Empire.
For researchers like César Oliveira (University of Évora, HERCULES Laboratory), cited by LiveSciencethis piece indicates a diffusion of quality technical objects in remote provinces. The model, its manufacture and its presence in Conimbriga reinforce the idea that this city, far from being marginal, was well integrated into the economic and administrative circuits of the Empire. The object demonstrates the circulation of metallurgical know-how and the mobility of Roman technical elites in the 1st century.
An ink of unexpected complexity for the time
What makes the Conimbriga inkwell exceptional is the ink residue preserved inside for almost 2000 years. Thanks to rare preservation conditions and a natural sealing of the pigment, the researchers were able to analyze the chemical composition of the ink at a molecular level. A battery of cutting-edge techniques was mobilized: pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS), nuclear magnetic resonance (NMR), X-ray fluorescence (XRF), infrared spectroscopy (FTIR) and Raman.
The results reveal a so-called “mixed ink” formulation, composed of several distinct ingredients. The main pigment is amorphous carbon black, resulting from the high temperature combustion of softwoods such as pine or fir. A marker called retene confirms this origin. But this black man is not alone. There is also bone black, identified by the presence of calcium phosphate, produced by the controlled calcination of bone materials.
© C. Oliveira et al., 2025
Extracted residues.
Another key discovery: the presence of ferric compounds characteristic of iron gall inks, although considered to be later. These inks, composed of tannic acid (from oak galls) and iron sulfate, offer better durability on supports. Finally, the analyzes identified binders. Beeswax played a stabilizing role, and animal fats (notably glue) improved the adhesion of the ink to the papyrus or parchment.
This formulation reveals advanced technical mastery. Each ingredient had a specific function in the use of the ink. Roman artisans manipulated much more advanced chemical knowledge than was supposed for this period.
Precise additive functions and ink designed to last
The combination of several types of pigments and binders in fact responds to practical requirements linked to administrative and technical uses of the time. The mixture reveals an empirical knowledge of the chemistry of materials, with attention paid to the hold, stability and durability of the line on different supports.
The very fine carbon black ensured a deep and saturated color. Bone black reinforced the opacity and modified the texture of the ink to achieve controlled fluidity. The addition of iron gall components increased resistance to humidity and friction. A particularly sought-after property for documents intended to circulate between provinces, or kept for a long time in archives.
Binders played a central role in the performance of the ink. Beeswax, identified by its lipid markers, served as a stabilizer and thickener. Once the ink was applied, it formed a thin protective layer, an effect comparable to a microscopic varnish. Animal fats, identified as monoacylglycerols and diacylglycerols, improved the adhesion and plasticity of the line, ensuring homogeneous application.
The researchers emphasize the balance of the formulation. The hypothesis of a volatile solvent, analogous to turpentine, remains put forward to explain the workability of the ink upon application, without compromising its fixation after drying. This detail echoes the resistant inks found at Vindolanda, near Hadrian's Wall. In short, we designed this ink to last.
Mobile technology in a well-connected Empire
The presence of a Biebrich-type inkwell in Conimbriga and such elaborate ink in a western province poses a central question. How could such advanced technology travel so far from the administrative heart of Rome? The answer lies in the existence of highly structured technical, commercial and human networks within the Roman Empire.
Objects like inkwells circulated with the people who used them: military engineers, administrators, civilian technicians. These professions required specific tools, sometimes standardized and produced in specialized centers. The study shows that Biebrich inkwells, originating from northern Italy and the Rhine region, are associated with these professional contexts. The fact that a copy is found in Conimbriga, more than 2000 kilometers away, testifies to a controlled mobility of equipment and knowledge.
The materials themselves (pigments, binders, metals) probably came from various sources. Lead, for example, could come from mines in Hispania. Beeswax, from local farms; iron sulfate, from workshops specializing in inks. This logistics involves well-established production and distribution circuits, even for objects as modest as an inkwell.
According to Vítor Dias, co-author and researcher at the Conimbriga Museum, “ this ink is not an isolated artifact. It is the result of shared knowledge, transferred and reinterpreted locally “. It reflects the Empire's ability to maintain a high level of technical coherence, including on its margins. Innovation, far from being confined to Rome, spread through this circulation of people, objects and recipes.
Source: Oliveira, C., et al. “Tracing literacy in Roman Conimbriga: insights from the metallurgy and ink of a Biebrich inkwell”. Archaeol Anthropol Sci 17, 216 (2025).
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