When Edgar Degas exhibited Portrait after a Costume Ball (Portrait of Madame Dietz-Monnin) at the 1879 Impressionist exhibition, critics were startled by its frankness and ambiguity. Unlike his celebrated ballet scenes, this portrait did not flatter its sitter, Madame Dietz-Monnin, a Parisian society figure. The painting’s ambiguous mood and unconventional finish sparked debate: was Degas mocking the rituals of high society, or capturing a fleeting psychological truth? The work stands as one of the few society portraits Degas completed, and its reception reflected the shifting boundaries of portraiture in late 19th-century Paris. The scene unfolds in the aftermath of a grand masquerade, with Madame Dietz-Monnin still in her elaborate costume, her mask now lowered.

She sits alone, her gaze distant and weary, as if the revelry has drained her. The heavy black domino cloak and mask in her lap signal both the festive occasion and the social roles she must play. Degas’s brushwork is loose and unfinished at the edges, focusing attention on her face, which is rendered with greater precision—a technique reminiscent of Édouard Manet’s psychological portraits.

The contrast between the theatrical costume and the sitter’s introspective expression hints at the tension between public persona and private self. The painting’s subsequent history is less eventful than its debut. It remained in private hands for many years, passing quietly through collections rather than public institutions. Its medium—often debated, as Degas experimented with oil, pastel, and mixed techniques—adds another layer of intrigue, with scholars still discussing the exact materials used.

Today, Portrait after a Costume Ball is recognized as a key work in Degas’s exploration of modern identity and social performance, bridging his interest in portraiture with his fascination for the spectacle of Parisian life.