Villa di Marlia, Lucca – A Fountain, John SInger Sargen, watercolor and gouache, 16 x 21 in. (40 x 53 cm). Link is to a larger image on Wikimedia Commons. Original is in the collection of the Museum of Fine Arts, Boston
I had the pleasure of seeing this beautiful Sargent watercolor, along with several similar pieces and a range of others, at a spectacular show at the Brooklyn Museum several years ago. Like a number of the other works in the show, it was easy to see that passages of lighter colors and white were painted over darker colors.
Sargent, like Homer and Turner and a number of other of their contemporary watercolorists, would carry a tube of “Chinese White” (zinc white) along with their kit, adding it to their lighter colors to make them opaque, essentially turning them into gouache.
It’s not as easy to see in flat photographs, but you can see it here in the white of the waterfall, for example.