Heritage Science: Conserving History

How Diamond is helping to preserve Scotland’s iconic historic buildings

History is all around us: and there are few more striking relics than the vast historic buildings that adorn ancient towns and cities in the UK and around the world. As of 2013, the UK tourism industry was estimated to be worth more than £125 billion. But work is needed to ensure the preservation of our cultural heritage – many of these iconic structures are at risk of being lost to time.
Over years of exposure, their basic materials become weakened, leading to deep structural damage. Uncovering the microscopic processes that lead to deterioration could help conservationists to develop a solution, but that’s no easy feat. Sometimes the damage goes so deep that it’s impossible to pick up on the surface.  And so scientists are looking to Diamond to help ensure that the architectural legacy of the past lives on.
In the 1800s, Scottish workers were employed to quarry huge amounts of sandstone from the surrounding landscape. The attractive stone was a rich local resource and it was used to build some of Scotland’s most recognisable buildings, bestowing the architecture of the country’s towns and cities with a distinctive character that attracts visitors from far afield. But there was an issue with the sandstone that would only become apparent centuries afterwards. Hidden deep under the surface, there were millions of minute pores, and these tiny holes would later create big problems for conservationists.
A fairly absorbent material, sandstone sucks in moisture from the surrounding atmosphere. Small particles of salt are also absorbed, either from the sea air or from de-icing salts used to make paths accessible in winter. This water and salt mixture then gathers in the pores of the material, where it slowly dries out. As this drying process takes place, the salt particles multiply and crystallise, forming growing concentrations of crystals inside the stone. This is bad news for historic buildings; the pressure from inside can cause them to weaken and eventually crumble. 
Dr Michael Drakopoulos, Principal Beamline Scientist on I12
But if scientists can learn more about how and why this process takes place, it may be possible for them to counteract the sandstone deterioration and recommend suitable materials to help repair the damage that has already been done. Because this entire process takes place within the stone, scientists can’t easily visualise it with standard lab equipment. That’s where Diamond comes in – its bright beams are about 10,000 times more powerful than visible light microscopes, giving scientists exactly what they need: the ability to see beneath the surface.
Supported by the conservation charity, Historic Scotland, Callum Graham is a University of Glasgow PhD student leading the research into preserving Scotland’s sandstone architecture. Callum is using Diamond to compare the differences between types of sandstones commonly used as replacements in damaged buildings: Locharbriggs and Cullalo sandstone, each quarried from different regions of Scotland.
Callum wants to explore differences in how the two stones respond to salt crystallisation damage. His aim is to find the perfect replacement stone to help remedy the architectural damage that has already occurred. To do this, Callum uses a technique more readily associated with hospitals than synchrotrons: computed tomography scanning, better known as CT scanning.
CT scanning is used to determine the density of a material. It works by exposing an object to X-rays and observing the amount of rays absorbed in different areas. This makes it medically useful in determining the site and shape of tumours or internal injuries. At Diamond, Callum uses the same technique to observe where pores exist within the Scottish sandstone and how salt crystals develop inside them.
This research has already yielded some important results. Using Diamond’s Joint Engineering and Environmental Processes beamline (I12), Callum has been able to see inside the stone and view the salt crystallisation process taking place in real time, observing the damage as it occurs. 
By scrutinising this process, Callum has discovered real differences in the way each stone distributes salt and moisture throughout the material. These differences are down to the stone’s pore structure, which is influenced by how the stone was formed. For instance, Locharbriggs stone formed approximately 265 million years ago during the Permian period, when Scotland was an extremely arid, desert-like environment. Because of this, Locharbriggs is a very porous stone. Its many small pores can be found within distinct layers in the stone. These layers prevent water from spreading so far, keeping it confined to smaller pores in the material.
Callum also found that smaller pores are filled with moisture before larger pores, with crystallisation occurring in these pores more quickly than previously thought. This is particularly important because it means that just a small amount of moisture and salt can rapidly cause permanent damage to the stone.
But there is an upside: with this information, Callum can recommend the best response from authorities to help preserve Scotland’s historic buildings. His research will help to identify types of replacement sandstone that are more resistant to damage, and will ensure that councils develop a better formula for de-icing salts that don’t have the same sort of detrimental impact.
Observing the impact of his work, Callum comments: “A historic building is so much more than bricks and mortar. It is a relic of our past and a reminder of where we have come from. To keep our cultural heritage alive, we need to understand more about the microscopic processes taking place way below the surface, and this depth of insight is only possible using the facilities based at a synchrotron.”
He continues: “I’m keen to share our experiences so that other people can appreciate how powerful the facilities at Diamond are, and how they are helping to solve real-world problems that are of great value to our national heritage.”
Our history is important. It links us back to our past, and we have a duty to preserve relics of our national heritage. Although they may seem like unlikely bedfellows, science plays a vital role in safeguarding history through the preservation of the monuments and artefacts from our collective past. And this is vital work. The lasting impact of Callum’s research will be the preservation of his ancestors’ architectural triumphs so that they can live on, to be enjoyed by future generations for years to come.