THE only two companies in the world which make curling stones are to

merge. Mauchline-based Andrew Kay and Company (Curling Stones) Ltd and

the Bonspiel Curling Stone Company Ltd of Wales are engaged in

negotiations to form one manufacturing operation, still to be named,

which will be based on the Ayrshire site.

Donald Macrae, manager of Kays, said yesterday: ''Both companies have

struggled. It's such a small market. The advantage is we will have just

one set of overheads.''

The Ayrshire company has been in business since 1888 and has recently

been investing in new equipment to update their traditional methods. The

Bonspiel Company have been making stones since 1978 at Deganwy in North

Wales, close to the source of one of the few quarries with rock suitable

for making curling stones.

The Welsh-made stones have acquired a better reputation in recent

years for their uniformity. Manager of the Bonspiel Company, Mike

Hughes, explained the benefits of co-operating. ''We have the modern

equipment, Kays have all the tradition.''

He might have added that only Kays have the rights to obtain granite

from Ailsa Craig, traditionally the source of the best rock. Indeed, at

the turn of the century, when all curlers owned their own stones, most

originated from the island in the Firth of Clyde. The quarries were

abandoned in 1973, but recently new methods have allowed smaller blocks

to be used again. Now, of course, one set of matched stones in an ice

rink serves the needs of many hundreds of curlers. The new rink at East

Kilbride was one of the first to see new stones of characteristic

green-speckled appearance of ''Common Ailsas'' curling down the ice.

The new company plans to concentrate on producing and marketing these

traditional stones in preference to the Welsh ''Blue Trevor'' which will

be gradually phased out. Most of the output will be for export.

The co-operation can only be good for curling, especially if it leads

to security in the supply of stones for a growing sport worldwide. On

the minus side, the future of the sport will rest entirely in the hands

of one small band of craftsmen in an Ayrshire village.