Isaac and Johann Isaac Hollandus

Isaac and Johann Isaac Hollandus were a 17th-century pseudonymous Dutch alchemist duo.^[1][2] It is not clear if they were father-and-son, brothers, or even the same person.^[3][1][2] The last part of their pseudonym, "Hollandus", simply referred to their home country of Holland.^[3] Some believed they were Jews, and have given this as a reason as to why they stayed anonymous.^[3] Isaac and Johann wrote "De Triplici Ordinari Exiliris et Lapidis Theoria" and "Mineralia Opera Sue de Lapide Philosophico".^[4]

They were originally believed to be from the 14th or 15th century, predating Paracelsus.^[1] They were among the most famous alchemists in Europe at one point in time.^[1] Johann von Löwenstern-Kunckel stated that "the incomparable Isaac Hollandus" "had more knowledge in his little finger than Van Helmont in his whole body".^[1] However, Isaac and Johann Isaac Hollandus fell out of favor in the early 20th century after it was concluded they were actually post-Paracelsus.^[1]