Seite - 168 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

168 Alteration study of silver inks on parchment ST5 could be applied smoothly to the parchment samples with the bamboo pen. It could be burnished without any smearing or powdering-off. As soon as the ink was dry, it ap- peared to be dark brownish-grey and glittery (Fig. 13). Reference ink ST6 Reference ink ST6 was produced using recipe CL M 24–29 (variation III 1 b, model 32)32. The recipe has its origins in the Lucca Manuscript and can therefore be dated to the end of the 7th or the beginning of the 8th century. Since sodium hydrogen carbonate (NaHCO3) was added to the silver powder, ST6 is categorised as a silver ink with non-metallic com- ponents. Cherry gum was used as a binder. Silver was refined by grinding silver leaves by hand using gum arabic as grinding aid. The aim was to investigage whether the method used for refining silver had an impact on the corrosion behaviour of the ink compared with that of ST3. In order to obtain a fine silver powder, 100 mg of silver leaves were ground by hand using gum arabic as grinding aid. Afterwards the powdery silver generated was washed three times and then dried. The fine silver powder was mixed with ten drops of wine vinegar (5 %) and ground in a mortar for five minutes causing the silver to turn blackish. After this second grinding process the silver was washed six times and then dried, whereby the colour of the powder changed to dark grey. 0.047 g NaHCO3 as well as seven drops of cherry gum (5 %) were added before use. ST6 could be applied to the parchment samples easily with the bamboo pen but smeared a little bit during burnishing. The dry reference ink appeared in a dark greenish-grey colour on purple parchment (Fig. 14). 32 Trost, 1991, p. 107. Fig. 14: Samples ST6_A; as de- scribed in fig. 9. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0