[Sound of bell ringing]
Dr Kate Giles (KG) – University of York
This project is about a problem with York Minster.
[Choir singing in the background]
The building is hundreds of years old and it has been eroding over centuries, and over those centuries lots of people have repaired it and we are just the latest phase of repair and restoration.
Science is helping us on the east front of York Minster because we’ve been able to observe over the past few decades, and even centuries, the magnesium limestone, the stone from which York Minster is made, but we’ve never been able to look at that in microscopic detail.
Dr Karen Wilson (KW) – University of Cardiff
What we are trying to apply to this problem are a range of x-ray techniques. A lot of people might be familiar with the idea of going to hospitals and getting their arms or their legs x-rayed after an injury, but these techniques can also be used to tell you about structure and chemical composition of materials. The techniques we’re using can actually tell you about the surface composition so we are able to probe specially those sites within the stone.
This is from the east front and its limestone but it’s a piece of 19th Century limestone and this shows that even 19th Century limestone decays very rapidly and you can see the level of decay here. This is one of the pieces that we are going to be looking at very closely in terms of the level of decay, what’s going on within the stone. And we are going to trial some of the conservation techniques that we’re using on the east front on this canopy in the stone yard.
Magnesium limestone is a wonderful building stone. It’s quarried in the area south of York so the stone that we have here comes from a whole range of quarries. It is a wonderful stone to carve. It is a beautiful colour this creamy limestone colour, but it’s also vulnerable to decay. Salts that are present are coming to the surface of the stone and you can see some of the salts here on the surface just between two blocks of stone coming out through a mortar joint. And those salts are normally washed off, but where they’re not washed off in an interior or more problematically on the exterior of a building, we have to deal with them and we have to think about the problems that they are creating.
[Choir singing in the background and priest giving sermon]
So the machine that we have been looking at is called an x-ray photo electron spectrometer. And this is a vacuum chamber which has vacuum pretty much the same level as found in space, and this will tell you about the composition of the surface of stones and then once we can identify what their composition is, we can then advise the stonemasons what the best material is to use in the restoration process.
The kinds of techniques that we’ll use to conserve this piece of stone are going to be using surface coatings. So a combination of lime, mortar, sour milk perhaps some yellow ochre just to create a surface that will protect it from the elements and that will become that sacrificial layer which, when the salts come out of the stone, they will go into that layer and it will be washed off, then it can be reapplied.
Once we understand how the stone starts to erode we can then advise the stonemasons and the people involved in the restoration process on either should they be replacing those materials, and if so, what materials would be better to use than ones that may have been used in unsuccessful restoration campaigns.
This work is very important for society because what we hope to be able to do is to advise the key people involved in the conservation of these buildings so that we can essentially secure the history of the UK, and these buildings can be maintained for future generations.
Limestone is one of the most important building stones in this country. It runs in a huge belt up from the south west of England right up to its outcrop here in the north east, and all limestone buildings are suffering from weathering and erosion and all of them have been restored over time.
[Sound of water and choir singing in the background]
So the work that we are doing here informs not just practice at cathedrals but could inform the routine maintenance, the day-to-day care, the restoration and conservation work at thousands of other historic buildings in the country. And it’s that hard science that we are bringing into the work at York Minster that we think is pretty unique, here and it’s a very interesting starting point for projects that might continue both here and elsewhere within the country.