This thesis stems from the mainstream notion that art conservation is a practice that stabilizes objects with well-defined properties, and it argues that idea is complexified when conservation practices are studied attentively. By considering concepts from new materialism – specifically becoming, agency and performativity – this analysis looks closely at the long conservation history of Rembrandt van Rijn’s canonical painting The Night Watch (1642), to center on the ontological tensions between states of change and permanency in which the painting comes to be. With a focus on process and materiality, this thesis begins with a historiographical exploration of the object in conservation theories, ranging from a positivist understanding of the work of art as a single object with defined physical properties, to a more constructivist definition, where the art object is understood as a multiplicity of forces. The text proceeds to introduce The Night Watch as an entity that transits between temporal ontologies of change and permanency, thus destabilizing its identity as a single artwork, positing it, rather, as an entity in transition, a becoming-object. Framing Rembrandt’s painting as process poses the question of who and what agents co-produce this process. Agency is demonstrated to be distributed amongst the artist, the materials of the painting itself, the conservators, and the technologies used in preservation practices: all forces that interact and mobilize one another in the process of materialization of The Night Watch. Accounting for the boundaries of The Night Watch not as fixed, but as being materialized, forces us to account for the practices – repetitions of doings – that perform those boundaries in the first place. The research and conservation project of the painting, Operation Night Watch, currently ongoing at the Rijksmuseum, displays all these agencies at play at the museum’s gallery. Understanding artworks as process ultimately has consequences not only for how an artwork is perceived, as fixed and eternal, but also for conservation ethics.