Surface effects affecting ac losses of Nb3Sn

60-Hz losses of Nb3Sn were found to be considerably reduced by anodizing. Anodizing followed by etching in dilute HF was also studied and found to be less effective because of increased surface roughness and hydrogen inclusion after prolonged contact with the acid. The increase of ac losses from contact with the bronze at the surface of Nb3Sn made by solid-state diffusion was investigated. Both a surface effect (proximity?) and thermal stress were found to contribute to the increased losses.