Seite - 79 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

Sophie Rabitsch, Inge Boesken Kanold, Christa Hofmann 79 purple (Fig. 2). The ground lichens were then removed by filtering the liquid through a nylon filter. Four batches of orchil made from Roccella tinctoria were prepared. The first two batches and the last batch delivered a satisfying result and turned purple. The third batch stayed brownish-red, even after six weeks. The batches were prepared on 19 July 2016, 3 November 2016, 10 March 2017 and 12 Mai 2017. The pH value of the undiluted dye ranged between 10.70 and 10.8581. The development of the dye took between five and six weeks. The dye could be used several times. Over a few months and up to one year, the dye spoiled, turned brown and developed a manure-like smell. The pH of the spoiled diluted dye was at 8.27. 81 The pH value was measured with a microprocessor pH meter (WTW, pH 537). Fig. 1: a) Roccella tinctoria, b) Lasallia pustulata. Fig. 2: Change of colour of orchil from green to purple during the fermentation process inside the lid of a glass jar. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0