Even though some critics do not look favorably on Vermeer's late works, they contain a number of stylistic and technical surprises. One of the most curious was the use of green earth in the shadows of the flesh tones of the female figures. The neck of the smiling young musician in The Guitar Player is a fine example. Green earth is readily visible in the right-hand side of the girl's neck and upper chest. Instead, the deep shadows of the face, very likely first laid in with green earth, have been painted over lightly with various shades of pink and red paint creating a silvery shadow that lightens the extensive core shadow of the head.
No one has been able to explain how Vermeer came upon this curious technique.
Green earth, a dull green pigment made of natural earth excavated in Italy and Cyprus (the best variety is said to comes from Verona), was widely employed by Italian masters in the 14th and early fifteenth century as a uniform base for painting flesh. Its purpose was to neutralize the white ground necessary to prepare wood panels for painting which made flesh tones applied upon it appear somewhat fiery. Once dry, the pink flesh tones were applied softly over the dull green base, giving the flesh, at least originally, an cool, pearlescent glow. Many of the delicate pink flesh tones of the period have since faded leaving the green earth ground exposed once again (see$$$$$).
This technique fell out of favor with the advent of oil painting and was rarely employed in the centuries that followed.
However, in a few paintings of the Utrecht School, green earth has been detected in the darker tones of the flesh. Some of the painters who belonged to this school had been to Italy to study painting where they may have come familiar with the technique, adapting it to their own expressive necessities.
Vermeer's utilization of this anachronistic technique would at least indirectly support a recent theory that Vermeer served his apprenticeship in Utrecht and not in Delft (it has been ruled out Vermeer had ever traveled to Italy). What is unexplainable is why he would have used green earth uniquely in his later works.