Curling Stone

The curling stone (or rock) used in the game weighs a maximum of 44 lb (19.96 kg) and is fitted with a handle on top allowing it to be rotated as it is released. If the handle is rotated away from the body the shot is said to be an out-turn, and if rotated across the body it is an in-turn.

A special feature of the rock is that its bottom is concave and the actual running surface of the rock is only 1/4 to 1/2 inch (6 to 12 mm) wide on the rim of the concave bottom. This small running surface allows the pebble applied to the ice to have an effect on the action of the rock. On properly prepared ice the rock's path will bend (curl) in the direction the front edge of the rock is turning, especially toward the end of its trip. The degree of curl depends on several factors, including the preparation of the ice and the flattening of common paths to the house during the game. Ice on which the rocks curl well is said to be swingy.

Although the rock is designed to be delivered by players grasping the handle as they slide down the ice, a special "delivery stick" may be used by players incapable of delivering the rock in this fashion. Such a stick is designed to attach to the handle so that it can be released without requiring the player to place a hand on the handle in a crouched position. This allows the game to be played by handicapped players, as well as those unable to crouch comfortably. According to the Canadian Curling Association Rules of Curling:

"The use of a curling aid commonly referred to as a "delivery stick" which enables the player to deliver a stone without placing a hand on the handle is considered acceptable."

A special handle has recently been developed for high-level tournament play, which integrates electronics to ensure a rock is released before it crosses the hog line. The handle is coated in metallic paint; the circuitry detects the relative charge of the thrower's hand contact to determine if they are still in contact, and a linear field is established at the hog line to indicate its location to the internal sensor. Lights at the base of the handle indicate whether contact was sustained past the line or not.

The Scots in particular believe that the best quality curling stones are made from a specific type of granite called "Ailsite", found on the Ailsa Craig, an island off the Ayrshire coast.