John Wilkinson made his fortune selling good quality goods made of iron and reached his limit of investment expansion. His expertise proved useful when he invested in many copper interests. In 1761 the Royal Navy clad the hull of the frigate with copper sheet to reduce the growth of marine biofouling and prevent attack by the Teredo shipworm. The drag from the hull growth cut the speed and the shipworm caused severe hull damage, especially in tropical waters. After the success of this work the Navy decreed that all ships should be clad and this created a large demand for copper that Wilkinson noted during his visits to shipyards. He bought shares in eight Cornish copper mines and met Thomas Williams, the 'Copper King' of the Parys Mountain mines in Anglesey. Besides supplying Williams with large quantities of plate and equipment, Wilkinson also supplied scrap for the process of recovery of copper from solution by cementation. Wilkinson bought a 1/16th share in the Mona Mine at Parys Mountain and shares in Williams industries at Holywell, Flintshire, St Helens, near Liverpool and Swansea, South Wales. Wilkinson and Williams worked together on several projects. They were amongst the first to issue trade tokens ('Willys' and 'Druids') to alleviate the shortage of small coins. Jointly they set up the Cornish Metal Company in 1785 as a marketing company for copper. Its aim was to ensure both a good return for the Cornish miners and a stable price for the users of copper. Warehouses were set up in Birmingham, London, Bristol and Liverpool.