Treated limestone samples undergoing natural weathering on site.

Our landscape of stone. We readily connect with the beautiful ones. Those in the historical palaces of the city, the parish churches of the older villages and those shaping the cliffs on the coast. We disconnect just as quickly however, when those stones powder, persistently shedding their skin, perhaps affecting us directly in our home or workspace.

Recognising that certain stone surfaces in historical architecture were weathering better than others, Italian scientists went about investigating these stones in the early 1980s. They looked at the intact stone patinas – a naturally formed surface – and compared these to the friable ones.

Taking into consideration stone types and environmental conditions, they discovered that natural processes transformed the surface of some limestones and marbles – both based on the element calcium – into a type of calcium salt (calcium oxalate). Although chemically very similar, this calcium salt is harder and less soluble than the base calcium (calcium carbonate), making it more resistant to deterioration processes.

The possibility of artificially inducing this transformation, which takes centuries to form naturally, was explored next. A treatment was developed and the successful artificial transformation was achieved through the surface application of an ammonium solution. This was applied to the stone’s surface, which reacts with the base calcium to produce the new calcium salt, and ammonia which evaporates from the stone.

Local research of this treatment on Maltese Globigerina Limestone started in the early 2000s where the transformation was found to be successful. The applicability of this treatment to historical local architecture was the subject of the research that followed where treatment was examined in the presence of sodium chloride which is the main salt present in seawater and one of the soluble salts ever-present in a small island environment like Malta.

Promising results prompted further studies that looked at treatment in the presence of other salts independently representing polluted and rural environments respectively. This led to a context-based research programme where treatment was evaluated in progression from a controlled laboratory environment to uncontrolled site conditions.

Ongoing research is focused on treatment and testing on site, on stone containing various salt mixtures and centred around three historical sites representative of coastal, urban and rural environments. This research is being carried out under the Reach High Scholars Programme, part-financed by the European Union, Operational Programme II – Cohesion Policy 2014-2020, ‘Investing in human capital to create more opportunities and promote the wellbeing of society’ – European Social Fund.

Did you know…

• Until the Lincoln Cathedral was built in England in 1311, the Great Pyramid of Giza held the title for the world’s highest man-made structure. It held the record for an unparalleled 3,871 years.

• The ocean is 3,682.2m deep on average. That’s about eight Empire State Buildings stacked on top of each other. The deepest part of the ocean, however, is about 11,030m. That’s more like 25 Empire State Buildings.

• Valletta was one of the first European cities to be constructed on an entirely new site.

• The highest volcano in the solar system isn’t on earth. That’s right, the highest volcano in the solar system isn’t on earth at all, but on Mars. Olympus Mons, on Mars, is a dormant giant shield volcano that rises to an elevation of 27km, and it measures 550km across.

For more trivia: www.um.edu.mt/think

Sound bites

• Where do dogs come from?: DNA analysis from a tooth fossil found in Siberia has revealed that it belongs to one of the oldest ancestors of the modern dog. The study places this dog fossil at 36,000 years old. Human domestication of dogs predates the beginning of agriculture by roughly 10,000 years but it is not very clear as to when the modern dog diverged from the wolf species. The discovered dog was named ‘Altai dog’ after the mountain on which it was discovered and resembles modern dogs much more than dog ancestors found in other regions. It is thought that dogs originated from the Middle East and East Asia but this and other discoveries shed light on a much richer history outside their main home.

www.sciencedaily.com/releases/2013/03/130306221139.htm

• Using submarine faults for earthquake prediction near Turkey: Earthquake prediction is an incredibly big problem that may never be solved. Saying that, not all earthquake zones are monitored in exactly the same way. An international team of researchers from Germany, France and Turkey have started testing a new monitoring technique near the large North Anatolian seismic fault, which marks the boundary between the Eurasian and Anatolian (Turkey) tectonic plates and moves at roughly two centimetres per year. It is also the cause of several large earthquakes in Turkey. However, one underwater segment of this fault, located a few tens of kilometres from Istanbul in the Sea of Marmara, appears to not have been seismically active since the 18th century. The team of researchers were intrigued and implemented a new technique where acoustic devices can be used to continuously monitor the movement of this segment. Using ten sound wave transponders the exact distance between different parts of the fault segment was measured for over a six month period. Thus far the results show no significant motion indicating that the section may be locked in place. Further monitoring will need to be done to find out whether this is the case.

www.sciencedaily.com/releases/2016/07/160713115102.htm