Cornelis was a very successful entrepreneur and that allowed him to become one of the most important art collectors from the Netherlands. Besides collecting drawings he was also interested in the scientific aspect of print making and experimented constantly in seeking new techniques to make etchings in a drawing alike style that reproduced his important collection. He experimented with printing in colour from several plates. He can be called a real inventor and brought the technique of printing to a new level. His working methods have been revealed by Th. Laurentius and catalogued in the work 'Cornelis Ploos van Amstel' Kunstverzamelaar en prentuitgever, published in 1980.
He was also Wood merchant and collector of old master drawings in Amsterdam. Devised new methods of reproducing drawings in prints ('prenttekening'), and published forty-six of them in twenty-one different sets between 1765-1787 in editions of 350 impressions, called 'Ectypa'; later bound together. He worked with other printmakers who were obliged to keep the newly invented techniques secret. Some of his assistants include Bernard Schreuder, Elisabeth van Woensel, Cornelis Buys, Cornelis Brouwer. His printer was Johannes Körlein. Son-in-law of Cornelis Troost