In the context of this artwork, analyze the Angel musicians of the Description.
The two paintings of angels that are associated with the Virgin of the Rocks and are in the National Gallery do not properly fulfil the original commission for two panels each showing four angels, singing on one side and playing musical instruments on the other. There are only two musicians, both turned the same direction and both playing musical instruments. One, in green, plays a vielle, and the other, in red, plays a lute. The positions of the feet and the drapery are similar, indicating that the same design has in part been utilised for both.  The angel in red is thought to be the work of Ambrogio de Predis.  The angel in green is the work of an unknown associate of Leonardo. The National Gallery suggests that it might be the work of Francesco Napoletano.In both cases the angel is standing in a grey painted niche. A reflectogram of the Angel in green with a Vielle revealed part of a painted landscape. The background of the Angel in red with a Lute could not be determined because the grey paint on that painting is thick and opaque.  While it is commonly thought that the two angel panels were originally placed on either side of the central panel, an article published by the National Gallery suggests that they were placed higher up on the altarpiece.
National Gallery Ambrogio de Predis panel Francesco Napoletano