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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www.yorkminster.com
