The dense, nonporous nature of blue hone granite prevents it from easily pitting, said Geoffrey Broadhurst, a curler with the Ardsley Curling Club in Ardsley-on-Hudson, New York. Pits occur when water infiltrates a stone's pores and then freezes. As the water expands, it cracks the rock.
"Until 30 years ago most indoor curling rinks did not have dehumidifiers to reduce frost on the ice. Also, when rocks sat on the ice, moisture would condense on the surface and penetrate into the granite pores. When the moisture froze, the granite would pit which is very bad for the bottom running surface," Broadhurst said.
Thompson, of the World Curling Federation, said some curling stones are made with granite from Trefor, Wales, but they are more prone to pitting than Ailsa Craig blue hone granite.
"The view of some experts is that in 20 to 30 years time, Ailsa Craig stones will probably last a bit longer," Thompson said. "There are Ailsa Craig curling stones in use today that were quarried 40 to 50 years ago. They have an extremely long life."
No suitable granite has been found for fashioning curling stones in North America, according to Broadhurst.
Today many curlers are moving toward stones that have striking bandsthe portion of the rock that bangs into other rocksmade from Trefor granites, which are more durable than Ailsa Craig blue hone granite. The same curlers prefer to use blue hone inserts for their stones' running surface.
Curling garnered significant television coverage during the 2002 Winter Olympic Games, and, as a result, the sport's popularity has surged. The growing interest has increased demand for curling stones, according to Patzke, the United States Curling Association spokesman.
Thompson, of the World Curling Federation, also noted a steady increase in demand for curling stones over the past six years. "Becoming an Olympic sport [in 1998] has been considerably effective. Coupled with that, curling is now appearing on TV today in a way it wasn't done in years gone by."
Six European countries joined the federation in December 2003, and Thompson cites exposure on the satellite-television sports channel Eurosport as the reason for its growing popularity. There are an estimated 1.5 million curlers worldwide.
Both the United States Curling Association and the World Curling Federation help newly formed clubs find used and refurbished stones for their members to throw until the clubs are on their feet and can afford their own stones. It can cost upward of U.S. $40,000 to fully outfit a club with stones.
To keep pace with the rising demand in curling stones, Kays of Scotland, an Ayrshire-based curling-stone company, received permission in 2001 to cart 1,500 tons (1,360 metric tons) of granite off of Ailsa Craig. The company has permission to return to the island on a periodic basis.
Lauder, of the Royal Society for the Protection of Birds, anticipates this relationship working to the benefit of the island's birds and curlers for years to come.
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