A great paper HERE by Paolo Molaro, carefully re-analysing the wash studies that Galileo made of the moon in 1609. The abstract reads:
With the manuscript of the Sidereus Nuncius preserved at the Biblioteca
Nazionale of Florence are included 7 watercolors of the Moon painted by Galileo
himself. We suggest that some of them, and in particular the drawing of the 30
Nov 1609 of the very first Moon's observations, illustrate the phenomenon of
the Earthshine of the Moon, which was discussed in some detail in the Sidereus
Nuncius to provide evidence of the similarity of Earth to other celestial
bodies. The watercolors were used as models for the engraving of the Moon in
the Sidereus but, surprisingly, the secondary light had not been reproduced.
Galileo may have decided for the inclusion of the passage on the Earthshine
only at a very late stage of the editorial process. Galileo's hesitation shows
how contentious was this issue already recognized as a possible discriminant
between the different systems of the world.