Cosimo III de' Medici, Grand Duke of Tuscany
Around 1686–87, he traveled with Adam Oortmans II to Italy, presumably via Vienna, as the emperor had been a client of his father. The journey continued towards Venice, where Jan wrote a letter to his mother in January 1689. In it he tells that there was no interest in his work there and that he would go to Florence, where the fame of his father's merit procured him a most honourable reception from Cosimo III de' Medici, Grand Duke of Tuscany.