Painting and Engraving
Before the advent of photography, engraving was a popular means of reproducing works of art, especially for inventory purposes. In the late 18th century, the Italian engraver Guglielmo Morghen made a faithful rendering of Erminia and the Shepherds, on which he inscribed a dedication to Don Vincenzo Aulicino of Naples, who likely owned the painting at that time.
Since no preparatory drawings for the painting are known to survive, this engraving may be our best clue to the composition's original appearance. Morghen's painstaking copy contains several details apparently covered up on Guercino's canvas by later overpainting and retouching. However, engravers have been known to add details to their subjects; only proper cleaning will reveal if this is the case with Erminia and the Shepherds.