AbstractThe present paper sums up some observations concerningsideledge in industrial aluminium cells. Furthermore, somelaboratory experiments with freeze formation on a gas-cooledcylinder (coldfinger) immersed into bath and metal are reported.The freeze formed during contact with bath did not melt awaywhen the coldfinger was lowered deep into the metal; this is inaccordance with a recently suggested hypothesis concerningsideledge facing the metal. It appeared, however, that the freezemelted away rapidly at a zone near the metal-bath interface, eventhough stirring or wave motion was not applied. This observationgave rise to a new interpretation of the conditions at the ledgemetal-bath boundary. It is suggested that the deep depression or“trench” formed at that zone is caused by a high heat transmissioncoefficient between metal and ledge at the meniscus formed nearthe ledge-metal-bath boundary.