This article presents the cleaning treatment carried out on a contemporary painting by Álvaro Lapa (1939-2006), a Portuguese artist, which belongs to the private loan collection of the National Museum of Contemporary Art – Chiado Museum. In this work, Gauguin (the wedding), dated from 1966, 1981 and 1995, the artist used synthetic paints of different nature. The chromatic layer presented a brownish layer, especially visible in the white colour areas, due to dirt accumulation. In the black areas small matt whitish spots were observed, which seem to started merging, giving form to a whitish film – a phenomenon commonly associated with the migration of surfactants. The diagnosis of the painting condition as well the technical and material study were performed. Interviews with the owner of the work and with the artist`s sons were conducted, in order to understand their opinion about the current painting`s appearance. In the end, the painting was subjected to an aqueous cleaning treatment, using an aqueous solution of tri-ammonium citrate.