En Plein Air is a French term, pronounced ‘plen-air’ and means ‘Outdoors’. Plein air painting is about leaving the four walls of your studio behind and experiencing painting and drawing in the landscape. The practice goes back for centuries but was truly made into an art form by the French Impressionists. Their desire to paint light and its changing, ephemeral qualities, coupled with the creation of transportable paint tubes and the box easel—the precursor to the plein air easels of today—allowed artists the freedom to paint “en plein air,” which is the French expression for “in the open air.” (Artists Network)
This changed in the 1800s, when tubes of oil paint became available allowing En plein air painting to become viable for many artists. In the 1830s, the Barbizon school in France that included Charles-François Daubigny and Théodore Rousseau used the practise to accurately depict the changing appearance of light as weather conditions altered.
In the early 1860s, four young painters: Claude Monet, Pierre-Auguste Renoir, Alfred Sisley and Frédéric Bazille, met whilst studying under the academic artist Charles Gleyre. They discovered that they shared an interest in painting landscape and contemporary life and they often ventured into the countryside together to paint in the open air. They discovered that they could paint in sunlight directly from nature and making use of the vivid synthetic pigments that were available they began to develop a lighter and brighter manner of painting that extended further the Realism of Gustave Courbet and the Barbizon school It was radical practise at its inception but by the later decades of the 19th-century the theory had been absorbed into normal artistic practise.
There were artists’ colonies across France such as the one at Étaples on the Côte d’Opal that included landscape impressionists Eugène Chigot and Henri Le Sidaner. The later artist specialised in translating nocturne light to canvas using oil and pastel.
The Macchiaioli were a group of Italian painters active in Tuscany in the second half of the nineteenth century, who, breaking with the antiquated conventions taught by the Italian academies of art, did much of their painting outdoors in order to capture natural light, shade, and colour. This practice relates the Macchiaioli to the French Impressionists who came to prominence a few years later, although the Macchiaioli pursued somewhat different purposes. Their movement began in Florence in the late 1850s.
In England the Newlyn School was also a major proponent of the technique in the latter 19th century. There were lesser known artist colonies practising , including a loose collective at Amberley in West Sussex centred around the Paris trained Edward Stott who produced atmospheric rural landscapes that were highly popular to some late Victorians.
The movement expanded to America, starting in California then moving to other American locales notable for their natural light qualities, including the Hudson River Valley in New York.