- Thursday, February 7, 2013
By John Martin
TLC Correspondent, London
In telling the story of the Good Samaritan my teetotalling headmaster at Sydney Cathedral School would wax eloquent about the medicinal properties of olive oil (“better for your skin than soap”) and wine (“the universal antiseptic”).
In those far-off days no-one would have dreamed that cathedrals might benefit from one or other of the remedies applied to the hapless Jerusalem-to-Jericho traveller. Acid rain, however, is prompting a quest for fresh ideas on how to preserve these ancient stones.
It’s been announced that York Minster, the second-largest gothic church in Europe, may shortly be coated in a layer of fat derived from olive oil. It’s all part of a growing trend of looking to the past for remedies to contemporary problems.
The Minster was built between 1220 and 1470 using magnesian limestone. Apparently the stone masons used to rub linseed oil into the blocks. The effect was to bind the calcium found in the limestone.
Now Cardiff University in Wales has developed a substance to form the proposed 21st-century protective layer. Chemist Karen Wilson said: "We went to the traditional idea but used olive oil. It forms a layer one molecule thick which stops water getting in — but is porous enough to let moisture escape."
In short the coating is waterproof but allows the Minster’s limestone to breathe. That is important. When impervious coatings are applied to stone buildings, over time it encourages growth of mould and efflorescence as the salt within the stone “‘flowers out.”
Research on the fabric of York Minister has uncovered one piece of environmental good news: air pollution in the city is down in recent times. Even so the fight to preserve this old pile continues. Salt weathering is a further hazard to be overcome; heritage expert Alex Horton, who has done a lot of work on the Minster, says it can only be arrested by inserting new stone.
Horton, who advised the Cardiff University team, says the proposed olive oil-based remedy “adds a further alternative option to the conservation palette, which may mean that more stonework can be retained during future programmes of repair.”
York Minster’s stones are becoming a collector’s item. Every stone removed in restoration work is carefully examined by an archaeologist, numbered, photographed and entered into a stone inventory. Carved stones such as grotesques or gargoyles are kept as part of the Minster’s stone display. Surplus stone is sold at auction and a buyer receives a certificate describing the stone’s previous use. The next auction is scheduled for Aug. 13.