In 1901 in Khotan on his way back from his first expedition to Central Asia, Aurel Stein tracked down and questioned Islum Akhun about his manuscript forgeries. These had been sold as genuine fragments to the Russian and British Consuls in Kashgar by Islam Akhun and his colleague for about a decade. Islum Akhun gave a detailed description of how he made the forgeries, including the dyeing process.
The sheets of modern Khotan paper were first dyed yellow or light brown by means of ‘Toghrugha’, a product of the Toghrak (or Toghraq) tree, which, when dissolved in water, gives a staining fluid.’ (M. Aurel Stein, Ancient Khotan, 512).
‘Toghraq’ is the Uygur name for the black poplar tree (Populus euphratica Oliv., Populus diversifolia Schrenk, Huyang 胡杨 in Chinese) and ‘Toghrugha’ refers to its sap. When the bark is cut the sap flows and forms into lumps. This has traditionally been used by the Uygurs as baking soda in cooking and in soap, and is listed as a medicine in Uygur and Chinese materia medica, but its use as a dye was also known.
IDP received samples of various parts of the Toghrak tree some years ago from a scholar in Xinjiang and recently Richard A. Laursen, Professor Emeritus in Bioorganic and Protein Chemistry at Boston University, agreed to analyze them. However, none were found to contain colorants. They did however produce a dark liquid that could have been used, like tea, to stain the paper brown.
Professor Laursen reports that there is also some evidence that the leaves are used to prepare a yellow dye, as chromatographic profiles of extracts of textiles from Cherchen and Loulan are similar to those from a related poplar tree from the region, Populus pruinosa Schrenk, and not to other known sources of yellow dyes.
For an audioboo of the sound of walking over autumnal Toghrak leaves on IDP's 2011 Field Trip on route back from Karadong, see below.