especially while dry cleaning or uncovering large areas of the paintings, may
pose a potential risk. Many fungi on wall paintings produce an enormous
amount of allergens, associated with dead cells according to their growing
conditions, but also toxins, such as cell wall toxins. Toxins from bacteria and
mycotoxins from fungi, have been obtained from some of the species
detected on wall paintings. Up to now there have been few investigations of
mycotoxin production at such sites. Recently, we could detect ochratoxin in
dust samples from St. Martin (Kreiensen-Greene), which has wall paintings
dating back to 1575 that were covered by lime wash in 1716 and uncovered
in 1977. The paintings are heavily overgrown by the fungus Aspergillus glau-
cus(Eurotium herbariorum) on an area of about 50 m^2 of original surface.
About 30% of Eurotium herbariorumisolates are known to be possible pro-
ducers of ochratoxin depending on how they are grown in the laboratory. In
experiments we could show that some isolates from other objects were also
capable of toxin production. To complete the investigations, dust samples
from the church were analyzed for ochratoxin and also turned out to contain
this mycotoxin (unpublished).
An even more dangerous situation arises in people with defective immune sys-
tems with thermotolerantfungi that are able to grow at temperatures as high
as 37°C (body temperature). These fungi are normally eliminated by the
human immune system, but if acquired by people with immune insufficiency,
they may be lethal. This topic is more or less completely unexplored; this
includes the extent to which these species are distributed at different sites,
their ability to produce mycotoxins under the prevailing climatic conditions
and on the substrates available. Therefore, this is likely to be one of the most
urgent questions to be worked out over the next few years. Until then, risk
should be avoided and conservation jobs with this type of high risk potential
should only be carried out with specific safety precautions.
4 Cleaning and Consolidation
Aspects of cleaning, as well as consolidation, have already been discussed when
dealing with the “barium method” of extraction and consolidation. So in this
section, cleaning in the context of salt extraction will not be referred to anymore.
However, there are other materials that become part of the paintings over
centuries of intensive use, as well as previous conservation treatments. Many
of these materials were applied as a consolidation treatment. This section will
therefore consider different consolidation methods before discussing how to
reduce their sometimes detrimental effects.
During consolidation of plaster and rendering, problems arising may be
the same as that of surface consolidation. However, to see these changes
beneath the paint layer in the early stages may be much more difficult. Modern
Wall Paintings: Aspects of Deterioration and Restoration 255