You say “sfumah-to,” I say “sfumay-to”

In the excel­lent Giotto to Durer: Early Renais­sance Paint­ing in the National Gallery, there is a descrip­tion of the paint­ing tech­nique Leonardo used for most of his later work, includ­ing the Mona Lisa. This tech­nique, which he called sfu­mato (“smoke-like”), cre­ates a sense of three-dimensional light and shade that is dif­fer­ent from that of his contemporaries.

I have seen ref­er­ences that said that the sfu­mato tech­nique was sim­ply to blend with the fin­gers. Leonardo cer­tainly did that, but you can find fin­ger­prints in oil paint­ings from before his birth, so fin­ger paint­ing is hardly unique to his style. Instead, it is based on his obser­va­tions of smoke. He noted that smoke. which is semi-opaque, looks white against a dark back­ground and dark against a light back­ground. So he decided to make use of the opti­cal prop­er­ties of lead white paint in a sim­i­lar man­ner. He would begin by apply­ing a very dark under­paint­ing in black, earth tones, and pos­si­bly a trans­par­ent bitu­mi­nous brown. This under­paint­ing was rather loose and thin, prob­a­bly diluted with naph­tha or oil of spike laven­der (almost no other 15^th cen­tury painters appear to have used sol­vents for paint­ing, so Leonardo is prob­a­bly the inven­tor of the washy under­paint­ing). He would then apply velat­uras over the dark under­paint­ing in muted col­ors mixed with white. The method pro­duces smoky, opales­cent tran­si­tions from dark to light that are quite beau­ti­ful and quite unlike other paint­ing in that period.

By the way, I want this Leonardo t-shirt.