<P> Artists have long painted outdoors , but in the mid-19th century , working in natural light became particularly important to the Barbizon school , Hudson River School , and Impressionists . The Newlyn School in England is considered another major proponent of the technique in the latter 19th century . The popularity of painting en plein air increased in the 1840s with the introduction of paints in tubes ( like those for toothpaste ) . Previously , painters made their own paints by grinding and mixing dry pigment powders with linseed oil . </P>
which group of artist is well known for painting en plein air
Barbizon school Hudson River School Impressionists The Newlyn School