“There was a hissing sound and a slight effervescence, and after fifteen minutes, Helvetius found that the lead had been transformed into the finest gold, which on cooling, glittered and shone as gold indeed. A goldsmith to whom he took this declared it to be the purest gold that he had ever seen and offered to buy it at fifty florins per ounce. Amongst others, the Controller of the Mint came to examine the gold and asked that a small part might be placed at his disposal for examination. Being put through the tests with aqua fortis and antimony it was pronounced pure gold of the finest quality.”
History of Alchemy from Ancient Egypt to Modern Times: Alchemy Rediscovered and Restored, by A. Cockren (1940).
17th century alchemist John Frederick Helvetius (Johann Friedrich Schweitzer(1625-1709)), Dutch physician and alchemical writer, claimed to have carried out the transmutation of lead into gold.