A set includes a molding device having a molding face having the same shape as a contact face of the blocking device. A removable overlay of rigid material has a first face attached to a first face of the semi-finished optical element and a second face opposite to the first face having the same shape as the contact face of the blocking device, the set being configured for having a first subset configuration in which the second face of the removable overlay is in molding contact with the molding face of the molding device, then a second subset configuration in which the second face of the removable overlay is free and then a third subset configuration in which the second face of the removable overlay is retained in contact with the contact face of the blocking device.