During this period he visited Wales where he took a particular interest in the copper industry. He spent some time at Parys Mountain on Anglesey, a major source of copper ore during the second half of the 18th century, and also at the works at Ravenhead and Stanley, both near St Helens, Merseyside, where ore from Parys Mountain was smelted. His findings were described in a publication that appeared in 1800 under the title Briefe über die Insel Anglesea : vorzüglich über das dasige Kupfer-Bergwerk und die dazu gehörigen Schmelzwerke und Fabriken (Leipzig : Crusius, 1800). His style has been described as 'cumbersome and pedantic' but his work still represents a useful source for the historians of technology and in particular of the mining and smelting of copper. An English translation appeared in 2007.