What Is Plein Air Painting?

There are some constraints...

90 minute watercolor done on site, Menton, France: The Bastion (now the Cocteau Museum), 2026

Forty-five years ago, in Rome, I was introduced to working on site in watercolor by Frank Montana, an architect trained in the Beaux Arts system in pre-War America. We didn’t call it plein air painting then, it was simply watercoloring on site. As a class exercise, it involved about two (or two and a half hours maximum) of work, the finished drawing turned in at the end of the class; we were expected to do the same out of class, and I don’t think any of us were tempted to work much longer than the in-class time frame—partly because we didn’t want to invest the time, and partly because Frank valued the immediacy, the energy, of the work done in one session in changing light. Being done in the springtime, even in Rome the light was not consistent day to day. Multiple day sessions for the same work on site never occurred to us.

I continued to work in watercolor on site in the years after that class, and only decades later did I start working in oil on site, partly under the inspiration of the wonderful artist John Smalley. John and I would also visit the National Gallery in London and look at the Gere collection of plein air oil paintings, and he would enlighten me about the issues and achievements of those artists. I discovered Corot, whom John appreciated for the rigorous formal structure of his on-site work. And I discovered Pierre-Henri Valenciennes, the eighteenth-century artist who codified the discipline of en plein air work in a treatise called  Elémens de perspective pratique, à l'usage des artistes : suivis de réflexions et conseils à un élève sur la peinture, et particulièrement sur le genre du paysage .

Valenciennes was explicit about the time constraints of plein air work, the roughly two-hour window within which the artist is looking at something like the same subject for the duration of the painting or drawing. Even so, the sun continually moves (from our point of view), and the biggest impact of that is the shape and position of shadows change constantly.

Valenciennes, Palatine Hill, Rome

Working on the same subject on site over multiple days allows for greater size and precision of the painting, both impossible within the two-hour window; working from photographs allows the same thing. There is nothing “wrong” about either of these ways of working, but they shouldn’t be called “plein air” painting. If you want to know what’s possible en plein air, stick to the time window. It changes your priorities, it forces you to edit and suggest rather than depict. It’s a discipline, and its primary value is not the work it generates, but the knowledge the artist gains about form, light, and structure when the mind concentrates intensely for a relatively brief period of time. Plein air work historically was not an end in itself; it was a form of research and practice. Our recent social media fetishizing of unrealistically precise plein air painting loses sight of the discipline’s economical beauty, its energy, immediacy and focus.