Friday 20th May 2011; Biodeterioration & Visit to Instituto Superiore per la Conservazione ed il Restauro

Week 6 of 12 
Module 4: Deterioration Mechanisms; Methods of Survey & Analysis


This morning we had a visit to the neighbouring Instituto Superiore per la Conservazione ed il Restauro. The Instituto was founded in 1939 and introduced a 'modern' concept of restoration considering 'historical criteria' and 'scientific research'; a transition from the old idea of 'artistic restoration'. We visited the stone conservation workshop and one of the materials analysis laboratories.

In the stone conservation workshop we were shown several of the sculptural projects currently being worked on including one which was a white marble sculpture of a figure, of which just the torso and lower body (minus feet or base) remained. The main issues faced with this sculpture included removing rusted iron pins from joints, repairing cracks and identifying how to reattach the upper and lower parts. In addition, the lack of a base creates a conservation debate as to how this sculpture can be displayed in a museum. Historically, holes were often drilled in the stumps of the legs and steel bars inserted and then attached to a base, elevating the sculpture to the appropriate proportional height. This however would cause irreversible damage to the stone and therefore is no longer considered a favourable option. Something I had not seen before having worked little with sculpture was the use of sand for supporting the stone. No base exists and so the legs have been placed into a tub of sand which allows both the sculpture to be stored without pressure on weak points and for it to be in a position that the torso can be tested above it for positioning etc (see image below).

The torso and lower half of a sculpture undergoing conservation in the Instituto stone conservation workshop.

We then visited one of the laboratories and were shown several of the pieces of instrumentation used for materials analysis. We were shown the thin section taken of a sample of paint that had been removed from a sculpture that we observed in the stone conservation workshop. This analysis was being carried out to identify the pigments used on the sculpture for identifying appropriate/compatible materials for cleaning the surface dirt without removing the paint (see images below).

The sculpture with traces of paint in the Instituto stone conservation workshop.

In the Instituto laboratory being shown the thin section of the paint removed from the sculpture pictured above using an optical microscope with the image shown on the screen behind.

In the second half of this morning and this afternoon Giulia Caneva, a biologist specialised in biodeterioration of monuments and plant ecology, came to talk to us on her subject. Biodeterioration is defined as 'any undesireable change in the properties of a given material that is caused by the activity of living organisms'. Giulia told us that in general biodeterioration stems from the utilisation of the substrate as a source of nourishment, however sometimes it is simply used as a living habitat. It is not always the mineral composition of a stone from which organisms can get nourishment, but in addition stone gains a build-up of organic material from dust, pollution and past restoration treatments. Biodeterioration can be conditioned by the 'characteristics of the material' or the 'characteristics of the environment'.

It can be easy to confuse some 'biofilms' (organic patinas) with chemical deposits/attack. The general rule seems to be that in a generally dry environment deposits are likely to be inorganic and those which have a constant feed of water will be organic.

In a masonry wall composed of a single stone type it often occurs that some blocks of stone will be entirely unaffected by a biofilm which is present across the rest of the wall (see image below). Studies that Giulia has carried out indicate that this is linked to the porosity of the stone and a very small reduction in porosity can make a particular stone an inhabitable environment for a specific organism. Different stone types are also more attractive habitats for different organisms- something that we can utilise for identifying different stone types in vernacular buildings and a tool that geologists use when carrying out field mapping.

Images in one of Giulia's slides showing the preferential colonisation of specific stones whilst leaving surrounding stones untouched.


It is worth noting that organisms are not always considered to be damaging to stonework, and even if they are it does not always mean that removal is the best solution. An extreme example of this would be where tree roots have taken over and moved through a structure; whilst still in place and continuing to grow, they will continue to cause damage to the structure, but they may also be holding the structure in the position that it currently stands and their removal could result in collapse.

Giulia made the point that unless it has already been decided that organisms should be removed from the surface of a stone (regardless of whether or not they are causing damage), it is not sufficient to limit oneself to generically identifying the taxonomic group (e.g lichens/algae/plants). This type of ecological study should not be seen as a stand-alone set of information and the skills of the biologist can add greatly to the understanding of the environment of the structure including variations in temperature, moisture and sunlight which could be inferred from the presence of the organisms present.