[152] Recent studies describe the chemical process of indigotin formation and the biotechnology of woad fermentation vats in more detail, see e.g., Philip John, “Indigo Reduction in the Woad Vat: A Medieval Biotechnology Revealed,” Biologist 53, no. 1 (February 2006): 31–35; Philip John, Stylianos Arghyros, and Nicholson, Sonja, “Indigo-Reducing Bacteria from the Medieval (Isatis Tinctoria L.) Vat: Some Aspects of Their Interaction with Indigo,” Dyes in History and Archeology 21 (2008): 45–49; Anna Hartl et al., “Searching for Blue: Experiments with Woad Fermentation Vats and an Explanation of the Colours through Dye Analysis,” Journal of Archaeological Science: Reports 2 (June 2015): 9–39; Dominique Cardon, Le monde des teintures naturelles (Paris: Belin, 2014), 329-332.