Curling stones, also known as rocks, are essential pieces of equipment used in the sport of curling. They are made of very specific materials and have unique properties that allow them to glide smoothly across the ice and be strategically positioned by curlers. But what exactly goes into making a curling stone?
The History of Curling Stones
Curling has ancient Scottish origins dating back to the 16th century or earlier. Originally, “stones” meant any stones found lying around that were flat enough to slide across ice. Over time, specialized stones were crafted for the sport.
Traditionally, curling stones were made from granite quarried on the Scottish island of Ailsa Craig. The island’s blue hone granite was ideal due to its low water absorption, consistent grain, and resistance to wear. Today, most curling stones still come from Ailsa Craig granite.
Granite Composition
The granite used for curling stones consists primarily of three minerals: quartz, feldspar, and mica. The abundance and combination of these minerals impact the properties of the finished stones.
Quartz is an extremely hard mineral that provides durability. Feldspar acts as a bonding agent. Mica flakes allow the granite to split along smooth planes, making it easier to craft into stones.
The specific granite composition differs across Ailsa Craig quarries. Different minerals in varying proportions contribute to subtle variances in the hardness and density of stones.
Shaping the Granite
Rough granite boulders from Ailsa Craig are first cut down into smaller blocks using diamond saws. These blocks are then shaped into circles on specialized lathes.
The final curling stones are approximately 5 inches thick and 12 inches in diameter. A concave running surface is carved into one side. The other side has a bottom with concentric circles to grip icy pebble.
After carving, the stones are polished. This involves sanding with progressively finer and finer abrasives. Polishing rounds out and hardens the running surface for maximum smoothness of glide.
Handles and Bottom Plates
Finishing steps transform the carved and polished granite into playable curling stones. First, a metal bolt is inserted for attaching a handle.
Handles allow players to grip and release the stones. Traditional handles have a rubber grip and plastic sides. Newer ergonomic handles aim for maximum wrist comfort and control.
A circular stainless steel or brass bottom plate is also affixed to the base of each stone. These removable plates protect the polished granite bottoms from wear and tear. Numbers or logos identify team stones.
Weight Range
The finished curling stones weigh between 38 and 44 pounds. This weight range was mandated in the late 1800s to standardize play between regions. Prior to that, stones could weigh from 6 pounds up to 50 pounds or more!
Heavier stones have more momentum and are less influenced by friction. Lighter stones are easier to control and aim. The weight standards ensure a consistent experience in the modern sport.
Inside the Stone
Thanks to their sturdy granite and refined shape, completed curling stones maintain their form and smoothness through years of play. A brand new stone is indistinguishable on the ice from a decades-old stone.
However, looks can be deceiving! Granite is actually slightly porous. Over time, water seeps into the interior of a stone and freezes. This gradually builds up within the stone’s pores.
Invisible internal ice alters the weight, balance, and glide factors of old stones. So while the outside appears pristine, the inside changes with use. Professional stones are periodically re-worked to restore their factory conditions.
New Materials
As Ailsa Craig granite reserves dwindle, new curling stone materials are being explored. Manufacturers now also use Trefor granite from Wales and Common Green granite from Scotland.
Composite stones made from quartz and ceramic particles in an epoxy resin matrix have been tested. These maintenance-free stones match traditional granite for hardness and consistency.
However, curling purists argue that nothing can truly replicate the feel of sliding across the ice with a time-honored Ailsa Craig granite stone passed down through generations.
Conclusion
Curling stones may appear simple, but their material composition and crafting process results in ideal properties for game play. Granite sourced from specific quarries, lathed into shape, finished with precision, and outfitted with handles allows players to execute finessed shots and complex strategies.
Understanding what goes into a curling stone – from raw granite to finished product – gives new insight and appreciation into this specialized sport equipment with a long history and promising future.