Pigeon Poop and Deterioration of Our Cultural Heritage

Image not mine - not being used for commercial purposes

Image not mine - not being used for commercial purposesAs if we need another reason to hate pigeons.

While researching a report as part of the MRes, I recently stumbled across a paper discussing the contribution of pigeon droppings to the deterioration of our cultural heritage. The course had taken us on a trip to a historic house to carry out a week-long field research project. I was looking at salts and their movement through porous solids, such as building stones, bricks and mortar and subsequently using the literature in trying to find out what salts I had discovered. Unfortunately, my results were inconclusive, as I suspect my FTIR ATR spectra were not clear enough and due to lack of time and sufficient sample size I was unable to chemically test all of the samples for sulphate, nitrate, ammonia, chloride or phosphate. It was however, likely that my samples contained primarily sulphate and/or nitrate, indicating a probably ground water source of moisture in the building.

The study was based in Madrid on the Panteón de Hombres Ilustres where there was a 30cm thick layer of poo! The sampling site was chosen due to the lack of exposure to rainfall, and the building material was a porous limestone which is a common building material worldwide. Pigeon droppings as a source of soluble salts had already been established, but it was not considered a major factor in building deterioration, leading to the further detailed study carried out in this paper.

When leached by water, pigeon droppings were found to form salt solutions with high acidity. The salts identified in the solutions included sulphates, chlorides, oxalates and the previously known phosphates and nitrates. Salts cause damage to buildings through crystallisation within the pores of the building materials when the water they were dissolved in evaporates. The cycles of evaporation and dissolution of the salts cause stress within the pores (they will expand when the salts crystallise) and eventually loose cohesion and can cause eventual loss of structural integrity of the building if left untreated. The water containing dissolved salts will either be from the ground or rainwater ingress due to problems with the roofing or foundations of the building. When the salts attack the mortars between stones and bricks you can generally see crumbling and flaking plaster and depending on the salt visible white efflorescence’s on indoor wall surfaces.

The paper discussed how sulphates can form as a result of reaction between atmospheric sulphur dioxide and building materials containing calcium and oxalates can be formed through lichen metabolism or applied organic patinas on the surface of the building material. The study demonstrated that these are not the only ways that these types of salts can be formed on the outside of buildings, with dissolved pigeon excrement possibly a much larger deterioration factor than previously thought. The presence of the salts as mentioned above was also accompanied by acidic solution, meaning that further deterioration of the limestone was apparent with etching of the surface of rock forming minerals such as calcite.

This leaves us with the question of how do we get rid of the damn pigeons? Not only are they unsightly and a health hazard but their poo is actively destroying out precious heritage! With a count of 5,000 pigeons in Trafalgar Square in London back in 2004 how do we manage this pest? Thankfully, this is not a question that is going completely unanswered, there have been many initiatives to help lower the pigeon count in London and undoubtedly elsewhere in the world (such as Edinburgh!), just Google ‘pigeon population London’ and you will find a whole host of articles relating to this. And if you have a chance to read, you have to love the Pigeon Blog.

The Problem with ‘Condition’ in Geological Collections

Does a crack matter? We know a painter (assuming that he’s not into new-modern-post-wierdness art) didn’t paint his mural with a cracked hole in the middle of it, but can we say the same for minerals? Why would it matter anyway? To someone viewing a mural, an essential piece of the story is missing, but with a mineral the exact chemical formula (lets not get technical here for those of you who are know-it-all’s, let’s make it simple!) is repeated everywhere, so what are we missing?

The term ‘in perpetuity’ is complex. To preserve something exactly as it is for ever is impossible, a problem all conservators and curators will be intimately familiar with. In heritage collections it is a fact that objects will become more fragile with time and the institution holding them will do their best to ensure the object is in the best condition relative to its original state (i.e. a solid, liquid or gas – a nice definition offered by Jonathan Ashley-Smith in one of our course lectures). This process may involve preventive conservation measures to ensure that the possibility of common problems affecting the condition, referred to as degradation, is limited. One of the first steps to carrying out preventive conservation is condition assessment.

In geological collections, you immediately come across some complex aspects regarding condition. To what state would we attempt to conserve this specimen – the time at which it was first formed on the surface of the earth or the point at which it enters a collection? How do we know that state unless we have documented evidence? Of course, in other heritage collections it is often possible to speculate about the original state, we assume what ceramic jars, oil paintings and tapestries should look like when they are first made. In these types of heritage collections it is also less difficult to say whether there has been alteration to the original state, dulling of a painting, breakage of ceramics or fraying of a tapestry all involve loss of an object’s integrity. When it comes to a geological specimen it is difficult to quantify where or when there is loss of integrity. Is it when it breaks, dulls, the label becomes damaged or all three? Even unlike other natural history collections where a beetle specimen may lose a wing and with it vital biological information, in geological collections defining state and detrimental alteration to an original state is difficult and may be impossible!

Although you can in some cases i.e. light degradation possibly get the ‘original’ mineral’s colour back, how applicable is this for condition assessments? I would say not very, since it should not be a time-consuming process. It may be possible to eventually make a comprehensive list of all the original colours of minerals with this problem, but then again who says this is the ‘pre-defined’ state you wish to assess from?

If the use of a specimen is to sit in a box all the time then fading is not a problem, but if you need these specimens for display or education their condition may drop – then again for a researcher the colour might not matter, and the crystal lattice and the chemical structure is more important. For a painting, it may be more important to see the original brushwork, the colours and vibrancy that the artist intended to appreciate the true meaning behind the image. For this to happen we need a starting point, an original state from which to infer condition, and then begin our conservation efforts.

What is my point?

Well, first off condition in geological collections should be measured with respect to the use a specimen is meant for. But secondly, can we even technically measure condition in geological collections at all? Is it possible to decide on an abstract original state for a mineral and assign condition accordingly? Then, how can we make these kinds of results comparable between collections or museums? Should there be some sort of globally defined original state for each mineral? Really, this is implausible and unlikely. Even if we can take a mineral back to its original colour, is that useful? What we want to know is how good it is for the uses we need it for – research, education, display. Just because a mineral specimen is not like it was when it came out of the ground does not make it automatically in bad condition, but it does throw up some interesting conceptual barriers to condition and its definition.

Tell me your thoughts on ‘condition’ and geological collections: leave a comment below!