With the resurgence of painting outdoors - "en plein air," a tribute to the French artists who popularized it - in the last few decades, many topics have become widely discussed as artists share their ideas and approaches. Probably the toughest endeavor known to artists is painting outdoors, with all of the hazards it invites. Artists have always traded thoughts on the gear they use - what easel, which brushes, what type of surface to paint on, the best brands of paint and the particular colors they prefer. It tends to get rather technical, but can be very helpful for approaching outdoor painting.
One item that is rarely, if ever, discussed is the outdoor artist's umbrella. Usually only mentioned in passing, umbrellas should be given a much more important place in the accoutrements of the plein air artist.
First and foremost, artists do not paint outdoors with the intention to copy Nature. (This could form a completely separate discussion - the influence of photography, television and movies on contemporary perceptions of what is "real.") Instead, what artists are attempting to paint are the color relationships. There is no possible way anyone can paint what they actually see - because they are using paint, a very limited resource, to try and imitate light, which is incredibly vast. So the broader the range of colors you have on your palette, the better chance you have to paint those color relationships - akin to having more keys on a piano with which to play your notes. Would a pianist prefer to play a piece by Mozart with just six piano keys, or a whole piano? Color is a language that every human being speaks; it is the artist's job to communicate.
Here is the main reason for working with an umbrella outdoors - the artist is attempting to paint those subtle color relationships amidst a tremendous amount of light. If you've walked out of your dark house into the bright morning sunlight, you understand how much light there is outdoors when you're forced to squint - because your eyes can't handle the intense change. After spending a little time outdoors, though, we adjust to the intense light, and it starts to look "normal," i.e. it doesn't seem as intense as it did initially (this same phenomenon is true for a lot of other situations, too). The challenge is painting color relationships that will recreate light in all of its innumerable manifestations - and then bring the painting indoors where it will ultimately be viewed, still retaining that sense of light.
Claude Monet used a large white umbrella outdoors which recreated the soft lighting that he used in his studio (Figs. 1 & 2), both of which allowed him to control the light. Joaquin Sorolla used umbrellas and large shades (Fig. 3) - especially when painting on the beach. Many of his beach paintings show evidence that he was working from underneath a shade of some sort. Charles Webster Hawthorne (1872-1930) and Henry Hensche (1899-1992), both known for their color, used umbrellas. Alson Skinner Clark worked under an umbrella when painting in the California desert (Fig. 4) and John Singer Sargent used two when he worked outdoors (Fig. 5) in Switzerland. Besides photographic evidence, upon encountering these artists' beautiful work in person, one realizes that they were obviously using umbrellas of one kind or another to control how they saw.
The modern artist's umbrella has improved - it still has a light exterior to reflect light/heat away, but now includes a dark interior to absorb reflected light/heat - allowing the artist to see their painting better, as well as keeping them cooler on hot days. (Other areas related to this are avoiding white palettes, and not wearing light or brightly colored clothing. Everything reflects!) The idea is to create the best situation outdoors in which to see your work, so that when you bring it inside, the colors are not dead. A translucent white umbrella outdoors does not block much light, so our eyes stay adjusted to the heightened intensity of outdoor light - and we paint too darkly. Though the photos above seem to feature primarily white umbrellas, they also appear to be much more opaque than today's white umbrellas, whose main purpose seems to be giving the artist an even sunburn.
The umbrella with a dark interior appears to have been a contribution by the Russians. Known for their beautiful and unique color, the idea was promoted by Sergei Bongart (1918-1985) who emigrated from Russia to the U.S. at about the time of World War II. So, to be able to paint great color, you first need to be able to see great color, and the umbrella is a must. Maybe two or three. As Sergei would say: "Co-lor must sing!"