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Extra virgin for York Minster

07 December 2012


LABORATORY tests on stone from York Minster have shown that a "cheap and simple" coating of a dressing made from olive oil could save York Minster's limestone fabric from eroding. The dressing repels water and the sulphurous pollutants that cause the stone to crumble.

The new coating is based on oleic acid, a constituent of olive oil. It was developed by Dr Karen Wilson and Professor Adam Lee of the School of Chemistry at Cardiff University, in conjunction with scientists at Iowa University, in the United States. Their findings are published in the online journal Scientific Reports.

"Like many buildings, York Minster is built essentially of magnesian limestone, and acid rain does not react very well with that," Professor Lee said. "They have been having problems with decay since the industrial revolution."

Pollutants collect on the limestone surface, and crystallise in small cracks and crevices that weaken the stone, which is then broken down and washed away by rain.

"We tried to develop some very cheap and simple coating methods, using conventionally occurring fatty acids like oleic acid, which is a common component of olive oil," Professor Lee said. "This would not be toxic, and could be applied across a huge building. It is a very cheap, viable, and non-toxic coating."

The oleic acid is mixed with a Teflon-like substance to repel water, a significant factor in stopping decay.

Previous restorers have experimented with protective compounds that ranged from egg white to linseed oil and vinegar, but they all failed because they sealed the stones too tightly, and prevented them "breathing". Also, when the coating cracked, mould and fungus got inside, causing more damage.

Dr Wilson said: "York Minster is eroding at a noticeable rate, and periodic renovations and attempted restoration efforts using the best materials available at the time have, in some cases, accelerated the decay. The next step is carrying out field studies by testing the Minster walls on site over the next few years."

The Minster is currently in the middle of a £23-million restoration programme, which has included replacing large quantities of stonework. The research - funded by the UK Science and Heritage Programme - could now be used to help conserve other historic limestone buildings around the world.


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