This method contrasts with studio painting or academic rules that might create a predetermined look. The theory of 'En plein air' painting is credited to Pierre-Henri de Valenciennes (1750–1819), first expounded in a treatise entitled Reflections and Advice to a Student on Painting, Particularly on Landscape (1800), where he developed the concept of landscape portraiture by which the artist paints directly onto canvas in situ within the landscape.
It enabled the artist to better capture the changing details of weather and light. The invention of portable canvases and easels allowed the practice to develop, particularly in France, and in the early 1830s the Barbizon school of painting in natural light was highly influential.
Amongst the most prominent features of this school were its tonal qualities, colour, loose brushwork, and softness of form. These were variants that were particularly relevant to the mid 19th-century Hudson River School and to Impressionism
Before the 19th century, artists had mixed their own paints from raw pigments that they often ground themselves from a variety of media. This had made for inconvenient portability and kept most painting activities confined to the studio.
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 practice 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 latter 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 among 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.
Why is the Plein-air principle of painting so attractive ? When we do research about a phenomenon Plein-air painting it is a line of painters from the nineteenth century that comes to our mind, and Claude Monet depictings of Notre Dame Cathedral is may be one of most illustrative as it plays around the same motif alternated with changements of light and color during different hours of a day. Claude Monet was a French Impressionist painter known for his commitment to plein air landscape painting and his use of light and color to express his perceptions of nature. Different artists has aborded differently this phenomenon, but in any cases works are showing freshness and luminosity effects. Alfred Sisley consistent of the Impressionists in his dedication to painting landscape en Plein-air, Charles-François Daubigny, landscape painter of the French Barbizon school who anticipated the Plein-air innovations of Impressionism, Marie Bracquemond, French painter, Henry Scott Tuke, English painter and photographer, Jean-Baptiste-Camille Corot, who simultaneously references the Neo-Classical tradition and anticipates the Plein-air innovations of Impressionism. Netherland painter Gerard Bilders was frequently painting in Plein-air with Dutch painter Anton Mauve, and Willem Maris around the village of Oosterbeek. Gabriele Münter was a German painter who was influenced by plein air painting and the Expressionist movement. Edgar Degas was a French painter known for his use of plein-air techniques and his focus on movement and the human form, especially in his Ballerinas. Eustache Deschamps was a French poet who wrote about the natural world and the beauty of the outdoors. Charles Baudelaire was a French poet who wrote about the city and the human experience. George Hendrik Breitner was a Dutch painter known for his use of plein air techniques and his focus on street scenes and harbor scenes.
From that line of traditional painting specifically executed in Plein-air we can speed our travel in time towards contemporary actions towards sustainability, recycling, upcycling, so we are jumping a gap of time towards contemporary artists. Norma De Saint Picman  is a French painter who linked the principles of plein air painting with ideas of  recycling and upcycling, specifically in relation to solar panels, starting from 2018 up to now, she has painted sixty panels, and presented them in exhibitions and cycles, at Contemporary Venice , 2019, Luce dell Eterno 2020, Artes Dei, Metamorphoses – The Worlds of Change , 2021, Noravisionsolar The Garden of Eden2021, Between Night and Day, 2022. Noravisionsolar project expanded further into Noravisionsolarmetaverse with different presentations in virtual galleries and NFT. 
Equipment and challenges
It was during the mid-19th century that the 'box easel', typically known as the 'French box easel' or 'field easel', was invented. It is uncertain who developed it, but these highly portable easels with telescopic legs and built-in paint box and palette made it easier to go into the forest and up the hillsides. Still made today, they remain a popular choice (even for home use) since they fold up to the size of a brief case and thus are easy to store.
The Pochade Box is a compact box that allows the artist to keep all their supplies and palette within the box and have the work on the inside of the lid. Some designs allow for a larger canvas which can be held by clamps built into the lid. There are designs which can also hold a few wet painting canvases or panels within the lid. These boxes have a rising popularity as while they are mainly used for plein air painting, they can also be used in the studio, home, or classroom. Since pochade boxes are mainly used for painting on location, the canvas or work surface may be small, usually not more than 20 inches (50 cm).
Challenges include the type of paint used to paint outdoors, animals, bugs, onlookers, and environmental conditions such as weather. Acrylic paint may harden and dry quickly in warm, sunny weather, and it cannot be reused. On the opposite side of the spectrum is the challenge of painting in moist or damp conditions with precipitation. The advent of plein air painting predated the invention of acrylics. The traditional and well-established method of painting en plein air incorporates the use of oil paint.
French impressionist painters such as Claude Monet, Camille Pissarro, Alfred Sisley, and Pierre-Auguste Renoir advocated plein air painting, and much of their work was done outdoors in the diffuse light of a large white umbrella. Claude Monet was an avid en plein air artist who deduced that to seize the closeness and likeness of an outside setting at a specific moment one had to be outside to do so rather than just paint an outside setting in their studio. In the second half of the 19th century and beginning of the 20th century in Russia, painters such as Vasily Polenov, Isaac Levitan, Valentin Serov, Konstantin Korovin and I. E. Grabar were known for painting en plein air.
But enthusiasts of plein air painting were not limited to the Old World. American impressionists too, such as those of the Old Lyme school, were avid painters en plein air. American impressionist painters noted for this style during this era included Guy Rose, Robert William Wood, Mary DeNeale Morgan, John Gamble, and Arthur Hill Gilbert. In Canada, the Group of Seven and Tom Thomson are examples of en plein air advocates.
Notable artists (selected)
- Peter Seitz Adams
- Frédéric Bazille
- Henri Biva
- Ralph Wallace Burton
- Mary Cassatt
- Jack Cassinetto
- William Merritt Chase
- Eugène Chigot
- Robert Clunie
- John Constable
- Lovis Corinth
- William Didier-Pouget
- Rackstraw Downes
- Carl Eytel
- Francesco Filippini
- David Gallup
- Antonio López García
- Arthur Hill Gilbert
- Vincent van Gogh
- I. E. Grabar
- George Hetzel
- Winslow Homer
- George Inness
- Konstantin Korovin
- Henri Le Sidaner
- Isaac Levitan
- Theodore Lukits
- The Macchiaioli
- Marvin Mangus
- Frederick McCubbin
- Stanisław Masłowski
- Willard Metcalf
- Claude Monet
- Berthe Morisot
- Edgar Payne
- Robert Antoine Pinchon
- Camille Pissarro
- William Preston Phelps
- Vasily Polenov
- Pierre-Auguste Renoir
- Tom Roberts
- Guy Rose
- John Singer Sargent
- Valentin Serov
- Alfred Sisley
- Matthew Smith
- Tim Solliday
- Joaquín Sorolla
- Edward Stott
- Arthur Streeton
- Anthony Thieme
- Tom Thomson
- Henry Scott Tuke
- Andrew Winter
- Robert William Wood
- Mary Agnes Yerkes
En plein air painters painting in Ringwood, New Jersey. Artists are using a French easel on the left of picture, and a Pochade box on the right.
Camille Pissarro, 1872, Hameau aux environs de Pontoise, oil on canvas, 54 × 74 cm, private collection
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