Recently I took a class with Bernard Dellario at the Winslow Art Center to explore the use of gouache as a field study medium.
While gouache is less frequently used than either sketching tools or transparent watercolors, it has the advantages of being opaque. This helps the artist in the field by allowing you to paint color-over color, regardless of value.
Dellario’s methodology includes two approaches: limited palette “wet gouache” method, where a few primary colors are mixed on a disposable palette, and a “dry” method, where a larger palette of dried “cakes” of color prepared ahead of time by the artist allow you to paint in a somewhat thinner manner.
I like both methods, and experimented with them recently. Here is an example of a pondside painting I did, first in gouache, then translating into oil in the studio: