During the last decade of the twentieth century, enzymes came into use for
reduction of such coatings, which had resulted in tension and later led to flaking.
First attempts were, for example, done on the Schongauer paintings at Breisach
(Germany) as an “impregnation lacquer”; applied in the 1950s, they resulted
in flaking and loss of the paint-layer (Figure 10). First scientific examinations
revealed a proteinaceous surface coating. The application of proteolytic
enzymes in poultices, however, did not give convincing results. After intensive
investigations, it turned out that the coating was a mixture of proteins and oily
components, which, of course, were not disintegrated by proteolytic enzymes.
Similar studies were part of a national research project in Lower Saxonia
funded by Deutsche Bundesstiftung Umwelt (AZ. 10631). To overcome the
problems mentioned above, and to avoid the application of organic solvents
(and health risks arising from them), a method was developed to reduce inap-
propriatecasein surface consolidations and allow the extraction of the free
amino acids during the application. No additional substrates were left in the
paintings and the effect of reduction can be easily controlled during the
application at site by non-destructive monitoring. This guarantees that paint-
ings containing casein or glue as original binding media, can be treated to
remove surface consolidants without damaging the original binding. In addi-
tion, the methods usedwere based on immobilized enzymes, which guaran-
tees that there will be no enzymatic activity left on the painting after the
application, since the bioactive molecules will be completely removed from
the wall, together with the membrane that was coated with the enzymes. This
may also be the only way to make good use of controlled microbial activity
during cleaning and consolidation of wall paintings. It should be mentioned,
Wall Paintings: Aspects of Deterioration and Restoration 261
Figure 10SEM of impregnation/consolidation at Schongauer paintings, Berisach, Germany