Abstract: A method of bonding laminations of a magnetic core is disclosed in which photo-resist material consisting of a co-polymer is applied as a film to a sheet of magnetic material to define lamination shapes to enable the laminations to be formed by etching. The film of photo-resist material on the laminations is then utilized to bond the laminations together in a stack. In order to permit the core to operate at temperatures higher than the softening temperature of the photo-resist material, the bonded stack is irradiated to cause changes to the bonding material such that the material does not soften at the operating temperature of the core.