Controlled enzymatic removal of damaging casein layers on medieval wall paintings

Abstract

A new, gentle enzymatic method was developed for a controlled removal of casein layers from medieval wall paintings. These casein layers were applied over the last 60 years on wall paintings in order to decrease substantial damage due to a peeling off of the frescoes from the roughcast surface due to environmental effects. However, due to the aging of the casein layers (at 40±50 years), a more drastic peeling occurred and the danger of total destruction of the wall paintings is severe. Thus, screening was performed to ®nd the most suitable enzyme for casein digestion. Alcalase 2.5 DX L was the most appropriate enzyme for an effective proteolysis reaction. The enzyme was immobilized on functionalized cellulose membrane. A membrane pad system with immobilized enzymes was developed which could be pressed on the casein layers on the wall painting. A controlled removal of the casein layers by proteolytic digestion was observed and it was possible to continuously wash off the hydrolyzed casein fragments from the wall painting surface by an aqueous carbonate buffer¯owing through the membrane pad. The removal and the digestion was monitored by reverse HPLC. Additionally, an on-line monitoring system was set up in order to continuously follow the casein layer removal and the digestion procedure directly on the wall painting. This technique is based on noninvasive 2D-¯uorescence monitoring. Optical ®ber systems were used to continuously monitor the¯uorescence intensity of casein-bound tryptophan. The off-line data were veri®ed with the on-line 2D-¯uorescence data. Based on the scienti®c result an appropriate technique for the controlled enzymatic removal of damaging casein layers on the surface of medieval wall paintings using immobilized enzyme is now available. It is now applied to remove such casein layers from medieval wall paintings in the Allerheiligen-Kapelle Cloister,

Back to the past—forever young: cutting-edge biochemical and microbiological tools for cultural heritage conservation

“…2; Table 1). In addition, biocleaning has been performed on stone artworks suffering from inaccurate or aged restoration intervention (Beutel et al 2002;Antonioli et al 2005) (Fig. 2; Table 1).…”

“…As previously mentioned, also stone artworks may suffer from inaccurate or aged restoration strategies. This was the case of two wall paintings covered by animal glue layers during restoration interventions which have been restored using different bio-based approaches as described by Beutel et al (2002) and Antonioli et al (2005), respectively (Table 1; Fig. 2).…”

“…Artworks may undergo a number of degradation and deterioration events, which widely vary depending on the specific artifact and the environment and conditions of conservation. These parameters may be extremely different if we consider, for instance, a book conserved at controlled temperature and humidity in a library or in a museum, or a stone statue or a cathedral, which are constantly exposed to weathering, pollution, microbial colonization (extensively reviewed in Mazzoli et al 2018), vandalism acts, etc… It is worth reminding that damaging of artworks is sometimes the effect of previous restoration interventions which underwent deterioration themselves during time, as in the case of glues applied to consolidate wall paintings or ancient textiles (Beutel et al 2002;Ferrari et al 2017).…”

A preliminary study on using enzymes in cleaning archaeological wood

“…Enzymes are often used in conservation paper (Banik, 2003;Grattan et al, 1987;Larminie, 1992), textiles (Ahmed, 2010), oil painting (Ramsay-O'Hoski, 1976), wall painting (Beutel et al, 2002;Ranalli et al, 2005), and stones (Cappitelli et al, 2007(Cappitelli et al, , 2006Saiz-Jimenez, 1997;Webster and May, 2006) to aid in cleaning and removal of dirt (Romão et al, 1990) and adhesive residues from previous repairs (Bellucci et al, 1999;Turner et al, 2005), but there is no previous study concerning the effect of enzymes on wood.…”

Use of lipase immobilized on celluse support for cleaning aged oil layers

“…Generally, hydrolases are used like amylases for polysaccharide degradation, [1][2][3] proteases for proteic material degradation 1,4 and lipases for fat material degradation in the restoration. 2,4,5 In particular lipases are able to degrade lipids, organic molecules made of triacylglycerols.…”