How painting in oils in front of the motif became popular fifty years before paint became available in tubes, and how it was done by the experts.
Desportes
From Velázquez’s pioneering sketches of 1630, through Valenciennes in 1780, to Constable, Corot, and Pissarro, Manet and John Singer Sargent in the late 19th century.
Introduced to Europe from the New World in the 16th century, Queen Elizabeth I loved them, and Jan Brueghel the elder and his son included them in many of their paintings.
It is hard to be sure when oil painting outdoors first started, but the oldest such paintings date from before 1700.
The Eclectic Light Company 