Forensic dye analysis in cultural heritage: Unraveling the authenticity of the earliest Persian knotted-pile silk carpet.

The use of forensic dye analysis in the field of cultural heritage is introduced, and a case study is presented determining the dating of a potentially important textile fragment from the Cleveland Museum of Art. The fragment, attributed on stylistic grounds to the 15th century, is purportedly the oldest surviving example of a Persian knotted-pile silk carpet. Raman spectroscopy combined with liquid chromatography - mass spectrometry determined the dyes used in the fragment include Metanil yellow, Congo red, and indigo, possibly in its synthetic form. Based on the dates of introduction for these dyes (1879, 1884, and 1897, respectively) and the first appearance of the textile fragment in 1928, the object is shown to be almost certainly a late 19th or early 20th century creation. Furthermore, impurities found in the red dye are suggested as potential markers of a pre-1970s synthetic route for manufacturing Congo red or possibly degraded Congo red due to environmental pollutants.