Examples of how molten braze metal may react with core alloys in practice are given and experiments to study some of the phenomenon are presented. In some cases this occurs by dissolution in a flowing melt, so-called 'guttering'. Another process involves removal of whole grains from the metal surface. This mechanism involves initially the formation of liquid metal films around grains as well as the migration of these films. The tendency for grains to be removed in this way depends on the energy and misorientation of the grain boundaries.