Abstract: A method of forming a portion of magnetic core from a plurality of magnetic ribbons using a former having an electrically conductive coil located about the former has following steps: locating an end of a stack of magnetic ribbon material substantially within the opening of the coil, locating the free end of said stack opposite the first end within the opening of the coil and then applying electric energy to said coil so as to produce a force that draws the ends of said magnetic ribbon towards each other to form the core. Also is disclosed a method for testing for the completion of the assembly of a magnetic core consisting of one or more magnetic ribbons comprising the steps of: measuring one or more electromagnetic characteristics including instantaneous value of the core current and voltage during the process of forming and comparing the said characteristics with a predetermined value.