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 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

Johannes Jacobus Bylaert (1734-1809)

Johannes Jacobus Bylaert (1734-1809). Bylaert, born in Rotterdam, had settled in Leiden as an engraver and a drawing teacher. He developed in the course of the '60s of the 18th century as one of the pioneers experimenting with 'prenttekeningen' or 'print-drawings', mostly done in crayon, a method for colour-printing. Some dozens of his 'print-drawings'  in crayon still exist today. Bylaert has explained his method in this bilingual French-Dutch book. The French text, printed on the pages facing the Dutch text, was translated by the teacher in languages L.G.F. Kerroux. A German translation appeared a year later in Leipzig as well in Amsterdam, under the title Neue Manier Kupferstiche von verschiedenen Farben zu verfertigen.
Bylaert's very important experiments with printing in more than one colour are to be seen in the context of other experiments, for instance those by the well-known Amsterdam merchant Cornelis Ploos van Amstel (1726-1798), who from ca. 1760 till 1787 published several of his famous 'facsimiles' of paintings.

RUITER NAAST PISSEND PAARD - 1776 Horseman besides a pissing horse Ruiter staand bij het hoofd van een pissend paard; op de achtergrond een rustende man met hond; in landschap met boom. Reference:                                        13,50 by 19,80 cm Rijksmuseum Amsterdam Inv. RP-P-1882-A-5552 Signed and dated by Bylaert  in pencil on backside : Door J.J. Bylaert in t'Koper gewerkt. naar Philips Wouverman . 1776 Design: Philips Wouverman (1619-1668) Engraver: Johannes Jacobus Bylaert (1734-1809) Technique: Etching in 'crayon' manner.