Throughout the fall of 2004, paintings conservators Joan Gorman and David Marquis of the Midwest Art Conservation Center conducted a major conservation treatment of Guercino's Erminia and the Shepherds during public viewing hours.     In 1999, the exhibition "Restoring a Masterwork" followed the process of conserving Giovanni Benedetto Castiglione's The Immaculate Conception with Saints Francis of Assisi and Anthony of Padua .