To create the smile sometimes described as "enigmatic", da Vinci employed a technique known as "sfumato", where outlines are blurred and the use of soft coloring and thin, translucent glazing allows forms to merge one into another creating a soft, sometimes mysterious or ethereal effect, in da Vinci's words, "in the manner of smoke without lines or borders". This technique was also used to create his subject's gauze-like veil, scarcely visible at first view. Da Vinci's active study of human anatomy didn't hurt his execution of this portrait, either, as is particularly noteworthy in the woman's hands.
The opposite of this, "chiaroscuro" is the use of paint to create the illusion of lighter parts emerging from darker areas, a technique that creates drama, and allows an artist to create a three-dimensional, sculptural effect on flat canvas. Use of this effect is seen in the hints of a rounded figure, the subject's skin juxtaposed against dark, heavy clothing draped around her.