Original poster: "Garry F. by way of Terry Fritz <twftesla-at-uswest-dot-net>" <garryfre-at-pacbell-dot-net> Only reasons I can think of as to why they are bare is because some plastics absorb some of the energy at the frequency of tesla coils. The other reason is a coil coated with a transparent coating looks neat! - From another wheel of time reader. ;-)