Combined, sequential dye analysis and radiocarbon dating of single ancient textile yarns from a Nazca tunic

Abstract

The accessioning of ancient textiles into museum collections often requires objective information regarding the object’s appropriateness and authenticity before purchase or gift acceptance. In the case of colored fabrics, the identification of dyestuffs consistent with the attributed time period and culture builds confidence and reduces the chances of the object being a simple forgery or fake produced using modern materials. Moreover, this information adds to the technical, cultural, and conservation knowledge regarding the object. Increasingly, chronometric age estimates in the form of radiocarbon dating are also needed to establish the object’s age or to further prove the materials match the purported date range of the textile. Each of these analyses consumes a small sample of the object, and typically they are conducted separately by different laboratories on individual sample yarns. This report demonstrates for the first time the sequential, combined analysis of dyes by liquid chromatography-diode array detection-mass spectrometry and radiocarbon dating of the same residual dye-extracted sample. The chemicals and solvents used in various dye extraction protocols are shown not to contaminate the extracted yarns for radiocarbon dating purposes. The approach was used in the authentication study of an ancient Nazca tunic made from natural fibers (wool) and dyes (indigoids, anthraquinones, and flavonoids) shown to have most likely been produced between 595 and 665 CE.

Dye Analysis of a 17th-Century Mattens Workshop Tapestry Based on Raphael’s Drawing, The Miraculous Draught of Fishes

“…Among the indigo-producing plants and dyed fibers examined by Laursen and Mouri [33], those that contain pseudoindirubin include woad (Isatin tinctoria), which is commonly found and historically widely used in Europe, rattlebox (Crotalaria incana) from the West Indies, and yangua (Cybistax antisyphylitica) from South America. Indeed, the present authors confirmed the presence of pseudoindirubin 1 and 2 along with indigotin and an unusually large chromatographic peak for indirubin in black and brown yarns from a late Nazca period woolen tunic that was radiocarbon dated to between 595 and 665 CE [21], consistent with the use of indigo from yangua in Pre-Columbian textiles [50]. Moreover, Laursen and Mouri found that pseudoindirubin 1 and 2 were absent in extracts of fiber dyed by Asian indigo dye plants such as Indian indigo (Indigofera tinctoria) and the Japanese ryukyu-ai (Strobilanthes cusia) and sukuno-ai (Polygonum tinctorium).…”

“…The detection of pseudoindirubins in approximately half of the blue samples from the tapestry studied here may indicate that indigo from different plant sources, probably both European woad together with Indian indigo, were used on the tapestry by the Mattens workshop. This discovery adds to the relatively sparse literature on this recently discovered, but potentially important, marker dye compound [21,33].…”

“…It is the second most common dyestuff found in this work. Indigo dyestuffs from several plants are known to contain the blue colorant indigotin (I3) as the major dye along with a small peak of its red isomer indirubin (I4) and a trace amount of their oxidation product isatin (I1) [18,21,33]. Additionally, of the eighteen samples found to contain indigotin in the samples studied here, the dye pseudoindirubin 1 could also be detected in nine [33].…”

“…The physiochemical data of the dye components used to guide identification of the dyestuffs from the tapestry are collected in Table 2. These data were culled from a combination of previous studies by this laboratory [17,[19][20][21], as well as data published by others, as discussed in Section 3. Dye identification was based mainly on the mass of molecular ions of the analytes detected supported by their UV-vis spectra when they could be measured.…”