Buried in the Chehrabad salt mine in north-western Iran are woolen garments made between 220 and 390 AD, during the Sassanid Empire. The garments once belonged to a man now known as Saltman, whose naturally mummified body was discovered in the Chehrabad mine in the early 1990s by miners. The mine’s extreme salinity preserved not only his remains but also his clothing, providing archaeologists with a rare glimpse into everyday life during the Sassanid period.
The garments have been underground for centuries and exposed to pressure and decay. So by all expectations, they could not have survived that long without degrading. Instead, they are still mostly intact, and their vivid red, yellow and brown colors haven't faded.
How is this possible?
Now a team of Iranian researchers found a possible explanation to this puzzle. Their findings, published in Nature Scientific Reports, explain why the colours have survived for more than 1,600 years and offer museums safer methods for studying and preserving fragile historical fabrics.
The researchers found strong molecular bonds between the dyes and both the amide regions of wool proteins and naturally occurring lipids within the fibres.[4] These bonds allowed dyes to penetrate deeply and resist degradation, even under harsh burial conditions.
This was established after analysing the garments and other remains using a technique called synchrotron-based Fourier-transform infrared (FTIR) spectroscopy — a non-destructive experiment that reveals chemical interactions at the molecular level.[5] By analysing how molecules vibrate when exposed to infrared light, synchrotron FTIR spectroscopy can detect subtle chemical signatures without damaging the sample — a crucial requirement when working with irreplaceable heritage objects.
"We could see how the dye molecules interacted directly with the protein structure of the wool,” said Mohammad Hossein Dehkordi, the study’s lead author. “These interactions helped lock the colour into the fibre. That sophistication is at the heart of a new study by a team of Iranian researchers that found the possible way to reveal how and why the dyes endured for so long”
To experts, the findings challenge long-held assumptions about ancient craftsmanship. “This research shows that ancient dyers had an intuitive understanding of materials that rivals modern practice,” said Kirsi Lorentz, Archeologist- cultural heritage expert at the Cyprus Institute. “They may not have described their work in molecular terms, but their techniques produced remarkably stable results.”
Elena Rossi, a textile archaeologist at the University of Bologna, not connected to the study sees wider implications. “Textiles are often dismissed as decorative or secondary,” she said. “But studies like this show they are technological objects. Dyeing required experimentation, detailed knowledge of natural resources and precise control of processes.”
The research also sheds light on trade and cultural exchange. Natural dyes were derived from plants, insects and minerals, many of which were regionally specific. Identifying their chemical fingerprints helps trace where materials originated and how knowledge travelled.
“Each dye tells a story,” said Gihan Kamel, the Principal Beamline scientist at the Infrared Beamline, SESAME. “It speaks of local environments, trade routes and shared technologies within the Sassanid world.” “This is a unique study I must say. Synchrotron FTIR allows us to extract rich chemical information while preserving the integrity of the artifact.” “For historical textiles, non-destructive analysis is not just preferable, it is mandatory,” she explained.
Beyond archaeology, the findings have practical implications for modern conservation. Understanding precisely how dyes bind to fibres can guide how textiles are stored, displayed and protected from light and humidity.
“This kind of molecular insight is invaluable for conservation,” said Lorentz. “It allows us to move from trial-and-error approaches to evidence-based preservation.”
The study also highlights the expanding role of large scientific facilities in historical research. Originally designed for physics and materials science, synchrotrons are increasingly being used to answer questions about the human past.
“When you look at these textiles,” said Rossi, “you are not just seeing fabric. You are seeing chemistry, skill and human choice woven together. Thanks to modern science, those ancient choices are finally visible again.”
Background.
The craft of dye-making is almost as old as clothing itself. Long before written records, early humans discovered that colour could be drawn from their surroundings — crushed leaves that stained skin, bark that bled brown into water, berries that left red marks on stone. What began as accidental encounters gradually became deliberate acts, marking the birth of dyeing as both a craft and a form of expression.
Over time, plants such as madder, indigo, saffron and weld provided reds, blues and yellows, while insects like cochineal and kermes yielded deep crimson tones. Minerals and earth pigments contributed blacks, browns and ochres. Fibres including wool, linen, cotton and silk were immersed in these extracts, often heated in clay or metal vessels. To make colours endure, ancient dyers developed mordents — substances such as alum, tannins or iron salts — that helped dyes bind to fibres. Though lacking chemical theory, their methods were refined through generations of observation and experimentation.
Across civilisations, from Egypt and Mesopotamia to China, the Andes and West Africa, dyeing became both a technical skill and a cultural language. Trade routes carried dyes and dyeing knowledge across continents, making colour one of the earliest global commodities. Tyrian purple, extracted from sea snails, became a symbol of imperial power, while indigo linked farmers, dyers and merchants from Africa to Asia.
The practice evolved alongside technology. Medieval guilds standardised techniques and guarded trade secrets, while global exploration in the early modern period expanded access to colour. A decisive shift came in the 19th century with the advent of synthetic dyes, beginning with William Henry Perkin’s accidental discovery of mauveine in 1856. Brighter, cheaper and more consistent, synthetic dyes transformed the textile industry and enabled mass production.
Today, dyeing sits at the intersection of tradition, science and sustainability. While industrial processes rely heavily on synthetic dyes engineered at the molecular level, renewed interest in natural dyes is driven by environmental and cultural concerns. Modern analytical tools — including synchrotron techniques — are now revealing the molecular sophistication embedded in ancient practices.
See “study “at: https://doi.org/10.1038/s41598-025-25106-0
See https://www.sciencedirect.com/topics/chemical-engineering/amide