BRITISH fine china maker Royal Doulton said yesterday it had agreed to buy Caithness Glass, which designs hand-made coloured glass giftware, for a maximum £5.47 million sterling. Royal Doulton, one of Waterford Wedgwood's main competitors in the international giftware market, said it already had irrevocable undertakings and commitments in respect of 85 per cent of the company and Caithness was recommending the offer to shareholders.