This paper presents a case study of the history, condition, and treatment of CH1 38 (Rho) Space Modulator (1984.42), a cellulose acetate work of art by Hungarian artist László Moholy-Nagy. The transparency and modernity of clear cellulose acetate substrate as a painting substrate was prized by the Constructivist artist, but the colour, shape and texture have changed dramatically as it has aged. Held in the collection of Historic New England’s Gropius House, this case study tracks the implementation of conservation best practices for cellulose acetate in the context of historic house museums since the 1980s. The physical changes and conservation efforts across nearly 40 years are documented, looking at how interventive and preventive conservation treatment, reproduction, display, and storage environments have impacted these changes. A corresponding environmental monitoring and identification project further explores issues and implementation of best practices for cellulose-based polymer objects that are accessible to small-sized historic house museums.