In negative ion surface conversion sources with barium converters sputtering of hydrogenous surface particles is believed to be the dominant negative ion production mechanism. In the work performed at the FOM‐Institute ion sputtering is also used as cleaning and diagnostic tool. This paper will review the work related to the sputtering mechanisms applied in the FOM surface conversion experiment over the last years. It will be shown that not only sputtering but also direct reflection and prompt rebound sputtering contribute to the negative ion formation on a barium surface.