He is perhaps most recognized for helping to build the collection of William Thompson Walters, for whom he purchased pieces by Honoré Daumier, Léon Gérôme, Jean-Baptiste-Camille Corot, Antoine-Louis Barye, Théodore Rousseau, and Paul Delaroche.

Lucas' responsibilities as an art dealer for these American business men also included overseeing commissions on their behalf, shipping out food packages, acting as a Parisian tour guide, and hosting dinner parties.

He also paid for the apartment of his long-term mistress Josephine Marchand and her servants; however, their relationship was discreet according to the expert Lilian Randall, who translated and decoded Lucas' diary.

[2] Lucas had a substantial collection, with a large number or prints by Eugène Delacroix, Édouard Manet, Mary Cassatt, and James Abbott McNeill Whistler.

[2] Many scholars, who especially appreciate Lucas' prints because they offer a comprehensive view of nineteenth-century graphic art, had enjoyed the convenience of the entire collection being housed in a single city.