<P> Kays of Scotland has been making curling stones in Mauchline, Ayrshire, since 1851 and has the exclusive rights to the Ailsa Craig granite, granted by the Marquess of Ailsa, whose family has owned the island since 1560 . According to the 1881 Census, Andrew Kay employed 30 people in his curling stone factory in Mauchline . The last harvest of Ailsa Craig granite by Kays took place in 2013, after a hiatus of 11 years; 2,000 tons were harvested, sufficient to fill anticipated orders through at least 2020 . Kays have been involved in providing curling stones for the Winter Olympics since Chamonix in 1924 and has been the exclusive manufacturer of curling stones for the Olympics since the 2006 Winter Olympics . </P> <P> Trefor granite comes from the Yr Eifl or Trefor Granite Quarry in the village of Trefor on the north coast of the Llŷn Peninsula in Gwynedd, Wales and has produced granite since 1850 . Trefor granite comes in shades of pink, blue and grey . The quarry supplies curling stone granite exclusively to the Canadian, Canada Curling Stone Co., which has been producing stones since 1992 and supplied the stones for the 2002 Winter Olympics . </P> <P> A handle is attached by a bolt running vertically through a hole in the centre of the stone . The handle allows the stone to be gripped and rotated upon release; on properly prepared ice the rotation will bend (curl) the path of the stone in the direction in which the front edge of the stone is turning, especially as the stone slows . Handles are coloured to identify each team, two popular colours in major tournaments being red and yellow . In competition, an electronic handle known as the eye on the hog may be fitted to detect hog line violations . This electronically detects whether the thrower's hand is in contact with the handle as it passes the hog line and indicates a violation by lights at the base of the handle . The eye on the hog eliminates human error and the need for hog line officials . It is mandatory in high - level national and international competition, but its cost, around US $650 each, currently puts it beyond the reach of most club curling . </P> <Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (August 2014) (Learn how and when to remove this template message) </Td> </Tr> </Table>

What are the lights on the curling stone
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