Tapestry is very important to the history of woven textiles. Egyptian cave paintings of weavers date them back to 3000 BC! Tapestries have been used for centuries as decorative art and for thermal insulation. Today, tapestries are produced on a small scale, and artisans focus on their restoration to keep the art form alive.
Fig.1 Dyed Yarn Samples (Photo courtesy of Dr. Paola Fermo)
Researchers in the Dipartimento di Chimica at the Università degli Studi di Milano (Milan, Italy) and the Fondazione ENAIP Lombardia (Botticino, Italy) are using analytical techniques including Raman spectroscopy to analyze the organic red dyes commonly used to dye the yarn of ancient tapestries. Understanding the chemical makeup of these tapestries can elucidate information such as provenance, the specific dye technique, and the dye and mordant used in the material. This information is vital to the further conservation and restoration of these tapestries, which are prone to color fading through a process called photodegradation. To study these materials, the researchers dyed wool and silk yarns following traditional recipes to be used as test standards (Figure 1) to learn the best techniques for identifying these colorants in ancient tapestries.
The i-Raman EX was used with a fiber optic probe to directly measure yarn samples dyed with kermes, cochineal, madder and brazilwood. The 1064 nm laser excitation is able to minimize fluorescence from the dye which might be observed with a higher energy laser. The spectra collected from the dyes were compared with spectral data available in literature data.
Figure 2. Raman Spectra of:
(a) silk dyed with brazilwood mordanted with aluminum potassium sulfate and potassium hydrogen tartrate;
(b) wool dyed with brazilwood mordanted with aluminum potassium sulfate and potassium hydrogen tartrate; and
(c) wool dyed with brazilwood mordanted with potassium dichromate and potassium hydrogen tartrate. Reproduced with permission from Fermo, et al. (2020).
Figure 2 presents the Raman spectra collected from silk and wool samples dyed with brazilwood mordanted with different salts. The peaks observed in the spectra are consistent with previously published Raman spectra of brazilwood.
This study proved the feasibility of using Raman spectroscopy to directly measure the traditional dyes used in tapestry. The authors are planning to test their methodology on samples from ancient tapestries and to develop an in-situ approach for nondestructive testing. Furthermore, artificial aging tests are planned for the test samples, and the analysis will be repeated to observe the difference between fresh and aged samples.
Click here to read the open-access article from the International Journal of Conservation Science.
To learn more about how B&W Tek instruments are used in art and archeology, go to https://bwtek.com/industries/art-archaeology/
Looking for something specific?
