‘Is this art?’ is a question often raised by museum visitors when encountering contemporary artworks. But what factors influence museum visitors’ judgement on contemporary art? To what extent do visitors’ prior knowledge, socio-demographic background, emotional experiences, and specific aspects of the artwork itself, influence their judgements? In the context of the Swiss National research project eMotion – Mapping Museum Experience, we investigated these questions experimentally. The site specific intervention created by the renown artist Nedko Solakov in the St. Gallen Fine Arts Museum allowed us to conduct such a concrete experiment. We interpreted the findings by statistical analyses of the data gathered from entry and exit questionnaires (n=291) in view of sociological art theories dominant in the last few decades. Against theoretical expectations, we found that the judgement art/non-art was driven by several factors not anticipated by those theories.