Almost two and a half thousand years old and still its colors shine: What a secret behind the brilliance of the oldest known knotted carpet in the world researchers have now uncovered. The wool was therefore fermented by a treatment with a yeast brew before dyeing, according to the examinations using X-ray fluorescence microscopy. As the researchers explain, the pretreatment, which is still practiced today, allows dyes to penetrate deeper into the fibers, which means that they fade less. The study shows that carpet manufacturers already made use of this effect at least 2400 years ago.
It is a showpiece of the Hermitage Museum in St. Petersburg: the so-called Pazyryk carpet is considered a particularly fine example of Central Asian craftsmanship from the Iron Age. It was discovered in a Kurgan tomb in the Altai Mountains in 1947 and dated to around 400 BC. In addition to its age, the carpet made of virgin wool has another exciting property: Although it was buried for almost two and a half millennia, the luminosity of its red, yellow and blue colors hardly seems to have faded. It was previously unclear which manufacturing technology made this possible.
Old and new fibers in sight
As part of their study, the researchers led by Andreas Späth from the Friedrich-Alexander-Universität Erlangen-Nürnberg have investigated the suspicion that fermentation is the reason for color fastness. This process is still used today by some traditional carpet manufacturers in Anatolia. So far, researchers have been able to trace fermentation technology back to the 17th century. Wool is stored in a suspension containing yeasts for three weeks before dyeing. The treatment leads to a change in the surface structure of the wool, which has a positive effect on the subsequent color absorption. However, the process is only used by experienced manufacturers, because mistakes can easily lead to destructive putrefaction processes.
During the investigations, the researchers compared wool fibers fermented and then dyed using the traditional method with samples of the Pazyryk carpet that were made available by the Hermitage Museum. They analyzed the fiber structures and the distribution of pigments along the cross-section of the wool fibers with the “PHOENIX” X-ray microscope from the Paul Scherrer Institute in Villigen, Switzerland. The focus was mainly on red wool fibers, as the pigment “Turkish red” has been used in Central Asia and the Middle East for centuries to achieve a characteristic red hue. It is an organometallic complex of alizarin, which is obtained from the roots of the madder, and aluminum.
Fermented wool is emerging
As the researchers report, freshly fermented wool can be clearly recognized in the photos by the characteristic erection of the outermost cuticle. In this way, the fermentation process increases the diffusion of the coloring pigments to the center of the wool fibers, which leads to significantly more brilliant and permanent colors, the scientists explain. However, the cuticle can fall off over time. It turned out that it had largely disappeared from the fibers of the Pazyryk carpet. However, the scientists were able to demonstrate the influence of fermentation through the comparisons. “The fermented wool fibers show a characteristic distribution of aluminum along the cross-section. We have now been able to detect the same pattern in the fibers from the Pazyryk carpet, ”reports Späth.
Thus they were able to confirm that the procedure was carried out as early as the 5th century BC. Was used. It is by far the earliest evidence of the fermentation technique of wool. The result shows how highly developed the techniques of textile craftsmen were at least 2,400 years ago, sum up Späth and his colleagues.
Source: Friedrich-Alexander-Universität Erlangen-Nürnberg, specialist article: Scientific Reports, doi: 10.1038 / s41598-021-84747-z
The Pazyryk Carpet in the State Hermitage Museum in St. Petersburg