Page - 90 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

90 Purple dyeing of parchment the more powerful the dye, then boiled in a leaden vessel. Next, five hundred pounds of dyestuff, diluted with an amphora of water, are subjected to an even and moderate heat by placing the vessels in a flue communicating with a distant furnace. Meanwhile the flesh, which necessarily adheres to the veins, is skimmed off, and a test is made about the tenth day by steeping a well-washed fleece in the liquefied contents of one of the vessels. The li- quid is then heated till the colour answers to expectations.114 However, neither Pliny nor other authors described the process sufficiently accurate enough to reconstruct it115. After the fall of the eastern Roman Empire in 1453 and with the discovery of different red colorants in the Middle Ages, the purple industry declined and technological knowledge was lost. The so-called cardinals’ purple was replaced by scarlet red and the garments were now dyed with kermes, an insect-based dye. Attempts at revival throughout the ages failed, Pliny’s observations were not understood and could not be replicated effectively116. In 2001, Inge Boesken Kanold succeeded in reconstructing a purple dyeing vat using fresh marine snails (Hexaplex trunculus) with the help of John Edmond’s booklet “Tyrian or Imperial Purple Dye, Historic Dyes Series No. 7”, at the Conservatoire des Ocres et de la Couleur in Roussillon, France. Preparation In May 2017, Inge Boesken Kanold and Sophie Rabitsch experimented with dyeing dif- ferent types of parchment with shellfish purple in Boesken Kanold’s studio in Lacoste, France. About 200 snails, Hexaplex trunculus, were bought at local fish markets (Fig. 15). These snails are frequently fished in the Mediterranean Sea and are sold as “escargot de mer”. Two kilograms of medium sized molluscs (about 100 animals) were needed for 1.5 litres of water. The colorant is located in the hypobranchial gland, which is situated in the big spiral of the snail shell. This gland contains the precursor of purple in the form of a colourless secretion117. To access the gland, the shells had to be cracked open, using a small stone or little hammer. The molluscs were frozen before the experiments, so they did not have to be crushed while still alive. The dyestuff undergoes a transformation: First, it is transparent, then quickly turns to yellow, then lime green, green blue and eventually purple due to the presence of oxygen. This process can be observed when cracking open 114 Boesken Kanold, 2017, pp. 67–68; Bailey, 1929. 115 Cardon, 2007, p. 553. 116 Boesken Kanold, 2017, p. 67. 117 Boesken Kanold, 2017, p. 69. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0