This technique is called sfumato (from the Italian for "foggy").    From Wordnik.com.  [PhysOrg.com - latest science and technology news stories] Reference

It is like a picture, or a succession of pictures, painted in what the Italians call the sfumato, or “smoky” manner.    From Wordnik.com.  [The Life and Genius of Nathaniel Hawthorne]

Vinci's brush strokes and a technique called sfumato, which he used to hide transitions between dark and light areas and to create realistic shading.    From Wordnik.com.  [Discover Blogs] Reference

Looking at the first picture, the word "sfumato" comes to mind.    From Wordnik.com.  [Edges in Moonlight] Reference

It's related to the concept of "sfumato," the smoky atmospherics made famous by Da Vinci in works like the Mona Lisa.    From Wordnik.com.  [Enveloping Tone] Reference

The technique, called "sfumato," allowed da Vinci to give outlines and contours a hazy quality and create an illusion of depth and shadow.    From Wordnik.com.  [X-ray study unlocks some of the 'Mona Lisa' magic] Reference

Actors seem to displace an image of mist — what the creative team calls "sfumato," after the Renaissance painting technique — as they move in front of it.    From Wordnik.com.  [A Digital Night at the Opera] Reference

In this context, the great merit of De Donder was that he extracted the entropy production out of this "sfumato" when related it in a precise way to the pace of a chemical reaction, through the use of a new function that he was to call "affinity" .3.    From Wordnik.com.  [Ilya Prigogine - Autobiography] Reference

The council had hoped to discover more details about Leonardo’s "sfumato" technique of subtly blending one tone into another, which the artist used to create a hazy effect.    From Wordnik.com.  [DaVinci’s Mona Lisa was a New Mother, Says Experts | Impact Lab] Reference

Especially the latter darkroom trick gives a very sfumato-like effect.    From Wordnik.com.  [Enveloping Tone] Reference

So, if you 'blur and bleed' your shadows, that's a good rule-of-thumb for a first attempt at sfumato, I think.    From Wordnik.com.  [Enveloping Tone] Reference

And this is a-- I guess it's still a mystery to the complete understanding of the technique he used called sfumato.    From Wordnik.com.  [CNN Transcript Sep 27, 2006] Reference

Inside, the men led Barrow past dormant wheeled and geared machines, like sleeping skeletons of iron dinosaurs in the inky sfumato warehouse darkness.    From Wordnik.com.  [The Art Thief] Reference

The multivocality of Shakespearean drama that conceals the author's point of view finds its counterpart in painting with Leonardo's invention of sfumato.    From Wordnik.com.  [Dictionary of the History of Ideas] Reference

They brought their specially developed high-tech tool into the museum when it was closed and studied the portraits 'faces, which are emblematic of sfumato.    From Wordnik.com.  [X-ray study unlocks some of the 'Mona Lisa' magic] Reference

And scientists are now saying they have cracked the mystery of the painting technique -- sfumato -- which consists of thin layers of paint and glaze, reappplied dozens of times.    From Wordnik.com.  [Joan Z. Shore: Da Vinci Decoded?] Reference

The British art historian has amassed dozens of prints -- portraits of eminent persons and domestic landscapes, notable for their sfumato tonality and abstract massing of forms -- that were made after 1850, when glass plates were rendering paper negatives obsolete.    From Wordnik.com.  [Season's Readings] Reference

Jacob Marrel's lush compositions always record the shared existence of plant and animal; most of his sfumato flowers are beaded with bright little insects, their movements carefully observed by a frog or lizard poised to pounce, or a spider sitting in its carefully strung web.    From Wordnik.com.  [The Flowering Genius of Maria Sibylla Merian] Reference

X-ray fluorescence spectroscopy unveils Da Vinci's astounding sfumato technique.    From Wordnik.com.  [WN.com - Business News] Reference

The details of how the sfumato technique worked have not been determined before.    From Wordnik.com.  [PhysOrg.com - latest science and technology news stories] Reference

Mantegna continued to render his paintings in this kind of pinpoint focus, even as Leonardo and Giovanni Bellini began to move to the more atmospheric effects of tonal color and sfumato.    From Wordnik.com.  [lines and colors :: a blog about drawing, painting, illustration, comics, concept art and other visual arts] Reference

Leonardo da Vinci was able to accomplish this using the sfumato technique, in which layers of paint are added on top of one another to create subtle changes in shading, but no harsh lines.    From Wordnik.com.  [Medlogs - Recent stories] Reference

From the notebooks 'celebration of an insatiably curious approach to life (curiositá) to the willingness to embrace uncertainty and paradox (sfumato) embodied in Mona Lisa's smile, these principles will seem at once intuitively familiar and surprisingly powerful.    From Wordnik.com.  [AvaxHome RSS:] Reference

Köklükaya's face, mysteriously resembling a sfumato Madonna painting from the Italian renaissance, suggests not only a particular mother, but also motherhood on a symbolical level, while the pensive gaze of the handsome Selcuk hints at his silent-waters-run-deep personality.    From Wordnik.com.  [Cineuropa] Reference

It’s the difference between revering a Madonna and Child as a devotional object and appreciating the artist’s use of perspective or sfumato.    From Wordnik.com.  [Starlight and Shadow] Reference

Leonardo da Vinci he excels in sfumato.    From Wordnik.com.  [The Catholic Encyclopedia, Volume 13: Revelation-Stock] Reference

About the sfumato.    From Wordnik.com.  [Enveloping Tone] Reference