In Virgin of the Rocks, how is the Louvre version of the The paintings elucidated?
The Virgin of the Rocks in the Louvre is considered by most art historians to be the earlier of the two and dates from around 1483–1486.  Most authorities agree that the work is entirely by Leonardo. It is about 8 cm (3 in) taller than the London version.  The first certain record of this picture dates from 1625, when it was in the French royal collection.  It is generally accepted that this painting was produced to fulfill a commission of 1483 in Milan.  It is hypothesised that this painting was privately sold by Leonardo and that the London version was painted at a later date to fill the commission. There are a number of other theories to explain the existence of two paintings.  This painting is regarded as a perfect example of Leonardo's "sfumato" technique.
Milan Louvre sfumato