tesla coil uses an air core. why?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Laurence Davis by way of Terry Fritz <twftesla-at-qwest-dot-net>" <meknar-at-hotmail-dot-com>

why does it use an air core?

i thought of several reasons.
  1)  core material choices don't operate well at the range of
      frequencies that tesla coils operate. (hysteresis loss?)
  2)  eddy current losses?

but what would happen should you decide to use a core?

1) perhaps nothing at all.  the hysteresis loss would further dampen
   the pulse from the primary.
2) the eddy current losses would further reduce the output efficency.

3) how about delaying the flux from the primary with a diamagnetic
   materaial?  perhaps wood?

have i missed any negatives that would prove air is the best core?

larry.