As you can imagine, there's a lot of physics involved in curling. Rotation speeds, angles, momentum transfer, friction analysis, ecetera. But would you also believe there's a bunch of chemistry at play here, too?
Uniforms are made of Lycra; curling sheet borders are made of high-density foam so that they remain relatively dry; and slider shoes are typically made with a Teflon sole, for the same reason frying pans use it. But there's even more chemistry at play in the ice, and the stones, especially.
The Scottish sport is played on ice kept at the perfect -5掳 C by networks of pipes pumping brine or antifreeze just below the surface. To keep the ice in ideal condition, technicians monitor temperature, humidity and even air quality via sensors embedded in the ice.
The water that's frozen to form the sheet isn't just tap water. It's carefully filtered to remove impurities and, if necessary, pH-balanced. The amount of total dissolved solids (TDS) in water, the softer the ice. With curling, the professional ice makers aim for 0鈥�10 parts per million (ppm) to make very hard ice with very little friction. Hockey and speed skating want their ice a bit softer, and figure skating the softest at 120鈥�150 ppm.
Curling sheets have pebbles of ice that are meticulously laid down by crews in two coats.
The first uses room temperature water, whereas the second uses warm water, creating pebbles that are a bit taller, leaving the first coat for once they wear away. Surfactants can even be used to 鈥渃reate a more durable pebble鈥�.
When it comes to curling stones, you may already know that all of the rock used in their creations comes from just two places: Trefor Granite Quarry in northern Wales, and Ailsa Craig, an island west of mainland Scotland. From this duopoly comes just four types of stone: Blue Hone and Common Green from the Scottish island, and Blue Trefor and Red Trefor from the Welsh quarry.
Blue Hone alone is considered ideal for the running band 鈥� the bottom of the curling stone that slides on the ice 鈥� because it's thought to chip less. But, Blue Hone is not a good material for the striking band 鈥� the part of the stone that hits other stones 鈥� because it's prone to developing crescent-shaped chips.
Research into why identified that it all comes mostly down to the mineral grain size in the rocks. Blue Hone has smaller grains that are mostly the same size, making them less likely to get plucked out by the ice than big grains, and the resulting hole is smaller if they do. It's also a relatively nonporous rock, which helps prevent cracks from ice forming in microscopic nicks.
Striking bands are best made out of the other three types of stone. They have a wider distribution of mineral grain sizes, which helps avoid crescent-shaped chips. While almost always called granite, the rocks that are made into curling stones aren't, strictly speaking, granite, but granitoids. As Derek Leung explained to me, 鈥淭he way we classify igneous intrusive rocks is based on the abundance of specific minerals in the rock. In the case of rocks that are chemically similar to granites (granitoids), the classification is based on the abundance of quartz, alkali feldspar, and plagioclase feldspar鈥�, he wrote. 鈥淏ased on this classification, the Ailsa Craig rocks can be classified as alkali feldspar quartz syenite, Blue Trefor = quartz monzogabbro, and Red Trefor = granite/granodiorite.鈥�
At over $600 each, it makes sense that a lot of research has gone into perfecting curling stones. But as Ailsa Craig is now a wildlife sanctuary, it may be that alternative sources of granitoids with as similar as possible compositions will be needed. Leung is hopeful that it might be found in Nova Scotia.
