Curling is a team sport with four players in each team. Both the teams took alternative rounds to slide the stones made from granite to the designated area (curling house). The stones are also regarded as rocks. The team with maximum stones passed closest to the marked ice region gets the maximum points and eventually wins the match. The players are required to sweep the ice sheet to decrease the friction of the stone so that it can travel in a straight line and a longer distance. As the sport requires a lot of strategies and techniques, it is also regarded as "chess on ice".
The curling stones are made of granite rock and weigh between 38 and 44 pounds. The sides of the stone are designed convex down to the ring and the inside of the ring is hollowed concave in order to clear the ice. The part of the stone which touches the ice at a specific angle is known as running band or surface. This flat surface is approx. 130 mm in diameter and has a width of 6.4 to 12.7 mm. Often, the stones exert a nominal pressure on the ice sheet which is approximately 0.1 to 0.16 MPa. This pressure, in turn, decreases the magnitude of friction coefficient leading to curling of the stone smoothly over the ice sheet.
The granite for manufacturing the stones is collected either from Ailsa Craig, situated in Ayrshire coast of Scotland or from Trefor Granite Quarry in Wales. Since 1851, Kays of Scotland manufactures curling stones and have the exclusive right of using the Ailsa Craig granite.
The curling stones contain a handle which attaches to the bolt via a hole present in the centre of the stone. The handle aids in suitably gripping and rotating it on the ice sheet. The handles are painted with different colours specific for each team. Usually, the makers use red and yellow colours to differentiate the stones for competitions.
Curling is an ancient sport that originated in the 16th century in Scotland. The first official record of curling stones was found in 1511 in the Scottish regions of Stirling and Perth. Later in the 1600s, stones with handles were introduced for smoother playing experience. In modern times, electronic handles are fitted which can easily detect the hog lines violations. The electronic handles on the stones are known as the "eye on the hog". It electronically detects any faulty start by the players and eliminates the risk of any human error as well as the requirement for hog line officials.
The modern stones have a total circumference of 91.44cm and a height of 11.43cm as specified by the WCF. The advanced technology has made the stone more feasible to use with a uniform surface. The major manufactures of curling stones are Kays of Scotland and Canada Curling Stone Company (which has exclusive rights to use Trefor Granite for the production of the stones).