Although art-based supervision often leads to supervisee disclosure, little is known about the experience, process, or contributions of such disclosure. We investigated the phenomenon of supervisee disclosure during "El Duende" Process Painting art-based group supervision using a qualitative study. JoHari's Window was used as a grounding model to describe content and structural analysis of the phenomenon of disclosure. Participants were supervisees (N = 21) in art-based supervision groups at 2 universities. Findings indicate that supervisee disclosure occurs in the artwork prior to conscious knowledge of the supervisee, and 3 precursors to increased self-awareness arise just prior to a disclosure. This suggests that mechanisms leading to disclosure occur during art making. Disclosure mechanisms have relevance for art therapy supervision and practice.